I think that this is a bug.
Timeline would be:
- The question was asked on Security Stack Exchange, where the asker had an account and where they left comments
- The question was then migrated to Super User, where the asker did not have an account
- The asker created an account after the migration, but the comments remain as they are, "unlinked" to their account
That's how it is.
There is an open feature-request to have that fixed up, where the comment author is linked back up to the owner.
But, like most comments, it's not really important to anything and could do well enough to just be deleted.
This is a known issue, see Comment authors are not getting migrated with status-deferred tag. The report is over four years old, and it had the "deferred" tag since 2014, so this is probably not getting fixed soon.