The same dns server (126.96.36.199 - ns1.dreamhost.com) is responding and I believe this is authoritative server
Just like with web servers, a single IP address could be hiding multiple DNS servers answering your requests. Even queries from the same location could be distributed to multiple nodes through a load-balancer or a multipath route. (Sometimes the "ns1" and "ns2" are entirely for show, with both leading to the same pool of servers.)
Yes, ideally all authoritative servers in the cluster should know the exact same data, but depending on how they're implemented, the cluster could have some servers temporarily out-of-sync with Dreamhost's authoritative database for various reasons. For example (entirely hypothetical – I don't know how Dreamhost's systems work), "reload" requests might be spread in time to reduce load on the database.
after I checked from different country (using cloud VPS) I got different pattern of answers
On a broader scale, when querying from different locations, BGP anycast could lead you to entirely different clusters. A good example is either public DNS resolvers or the root servers – there are many instances of 188.8.131.52 around the world, and there are many instances of "f.root-servers.net". If Dreamhost uses anycast to host "ns1" at multiple physical locations (which they probably do, for reduced latency), then it is even more likely that they will be out-of-sync for a short period of time after you make changes. (That's one area where "DNS propagation" isn't a lie.)
Many DNS servers support the special
id.server queries to which they reply using their individual names. Try this from different locations:
dig +short @ns1.dreamhost.com hostname.bind. chaos txt
But overall, none of the above really changes things – your problem is not much different from having actually separate servers and keeping them in sync. For example, even if you just had ordinary ns1/ns2/ns3 servers using traditional DNS AXFR replication, whenever new data is loaded into the master server it can take a few seconds for it to send out NOTIFYs to replicas and for them to transfer the changes. Resolvers looking at your NS records are completely unaware of this and could randomly select either a server that already has the new data or a server that does not.
So regardless of how your DNS host works and how many servers it has, you should never expect updates to be 100% instant; find out whether the provider publishes the expected time, or just wait an arbitrary 5 or 10 seconds.