If a hard drive caused "bus errors", should its SMART attributes show problems?

The machine shows "ATA bus errors" occasionally, and has to be rebooted:

[24028.505239] ata1.00: exception Emask 0x10 SAct 0x0 SErr 0x48d0002 action 0xe frozen
[24028.505249] ata1.00: irq_stat 0x08400040, interface fatal error, connection status changed
[24028.505254] ata1: SError: { RecovComm PHYRdyChg CommWake 10B8B LinkSeq DevExch }
[24028.505258] ata1.00: failed command: FLUSH CACHE EXT
[24028.505266] ata1.00: cmd ea/00:00:00:00:00/00:00:00:00:00/a0 tag 20
                        res 50/00:18:50:6b:d9/00:00:eb:00:00/40 Emask 0x10 (ATA bus error)
[24028.505269] ata1.00: status: { DRDY }
[24028.505276] ata1: hard resetting link
[24032.757212] ata1: SATA link up 6.0 Gbps (SStatus 133 SControl 300)
[24032.757615] ata1.00: both IDENTIFYs aborted, assuming NODEV
[24032.757620] ata1.00: revalidation failed (errno=-2)

If, after rebooting, I run smartctl -t short /dev/sda, smartctl -H /dev/sda says it passed.

From smartctl -a /dev/sda:

Vendor Specific SMART Attributes with Thresholds:
ID# ATTRIBUTE_NAME          FLAG     VALUE WORST THRESH TYPE      UPDATED  WHEN_FAILED RAW_VALUE
  1 Raw_Read_Error_Rate     0x000b   100   100   016    Pre-fail  Always       -       0
  2 Throughput_Performance  0x0005   136   136   054    Pre-fail  Offline      -       80
  3 Spin_Up_Time            0x0007   253   253   024    Pre-fail  Always       -       176 (Average 237)
  4 Start_Stop_Count        0x0012   100   100   000    Old_age   Always       -       233
  5 Reallocated_Sector_Ct   0x0033   100   100   005    Pre-fail  Always       -       0
  7 Seek_Error_Rate         0x000b   100   100   067    Pre-fail  Always       -       0
  8 Seek_Time_Performance   0x0005   124   124   020    Pre-fail  Offline      -       33
  9 Power_On_Hours          0x0012   091   091   000    Old_age   Always       -       63994
 10 Spin_Retry_Count        0x0013   100   100   060    Pre-fail  Always       -       0
 12 Power_Cycle_Count       0x0032   100   100   000    Old_age   Always       -       204
192 Power-Off_Retract_Count 0x0032   098   098   000    Old_age   Always       -       2756
193 Load_Cycle_Count        0x0012   098   098   000    Old_age   Always       -       2756
194 Temperature_Celsius     0x0002   142   142   000    Old_age   Always       -       42 (Min/Max 23/52)
196 Reallocated_Event_Count 0x0032   100   100   000    Old_age   Always       -       0
197 Current_Pending_Sector  0x0022   100   100   000    Old_age   Always       -       0
198 Offline_Uncorrectable   0x0008   100   100   000    Old_age   Offline      -       0
199 UDMA_CRC_Error_Count    0x000a   200   200   000    Old_age   Always       -       0

SMART Error Log Version: 1
No Errors Logged

I know that sometimes (25% of cases) hard drives fail suddenly, and without ever reporting any problems in SMART. But here, I'm already seeing errors. Does the fact that SMART is silent prove that the hard drive is not the source of these errors?

Hardware: SuperMicro motherboard and an HGST Deskstar NAS hard drive.

There are multiple components between the hard drive and the operating system, and any one of them can fail. Typically the errors you show are caused by errors in the hard drive.

However, lack of any logged errors in SMART is a likely sign that the hard drive itself is healthy. So one of the other components in the chain may have a problem.

Here's a checklist that may help:

• Make sure the drive is well seated and that all cables are fully engaged with the drive.
• If the drive is plugged into a riser board, make sure all the cables on the riser board are well seated.
• Make sure any data cables involved are in good condition, free of nicks, kinks, hard twists, and stretches
• Make sure the data cables are well seated in the motherboard or disk controller
• If you are using an add on disk controller, make sure it is well seated in the motherboard
• If in doubt that anything is not fully seated (assuming it isn't screwed in and difficult to remove), it may help to reseat it by removing it, checking the socket for dust, and plugging it back in, making sure it is fully seated.

After you have checked all that and the error is still occurring, then further diagnostics will need to be done to determine which of the above components is failing. If possible, swapping drive locations or swapping cables between motherboard or disk controller ports may help isolate it further. A disk controller with a bad chip can also cause issues like this, but it may be possible to diagnose this only by swapping with another controller.

It may also help to run an actual diagnostic on the drive (with smartctl -t short for instance and then wait for it to finish and check with smartctl -a to see if it is done or has errors), just to make sure it really isn't the drive.