If the file displayed is inside /snap/chromium/ then it comes from the official package, built by the Ubuntu developers, so on that alone, it's genuine. We know this because the /snap/chromium/ is the snap package mounted from an unmodified read-only file delivered from the snap store.
Looking at the file in question, it does indeed look like this:
Password storage in Chromium
Password storage via the Gnome keyring has been fixed, but for it to work, you have to rename your old ~/snap/chromium/common/chromium/Default/Login Data file so that a new, working one can replace it.
We suggest you to rename it to Login Data.old. You can do so through your file manager or by opening a terminal and entering
cd ~/snap/chromium/common/chromium/Default/
mv "Login Data" "Login Data.old"
This way, in case something goes wrong (and please file a bug report in Launchpad if so), you can always reverse the action by renaming the file back to Login Data.
Disable this message by creating the file ~/snap/chromium/common/chromium/Default/Login Data.old.
The logic around when this is displayed was introduced* recently.
*If that link doesn't work (issue caused by the tilde), copy and paste in the URL bar the address below:
https://git.launchpad.net/~chromium-team/chromium-browser/+git/snap-from-source/commit/?id=783497f8517231dd0b473300a6b1e66762b6bbbf
