In 2003 a "secret" feature was introduced. When an account with bot flag performs a rollback, then reverted edit(s) get retroactively marked as if they were performed by a bot (@tstarling, r2203, 036ff960ce)
I assume the reason for this feature was as a first step towards a patrol system in which Special:RecentChanges could be reduced over time, starting with retroactively hiding obvious vandalism. I also assume that at this time there must'be been a way already to hide bot edits, and this was simply the hammer available to hit the nail with.
The next year in 2004, the first parts of the rc_patrolled feature were introduced (Arne Heizmann, r4619, 075396a961).
In 2005-2006, as part of improving the patrol system for wider use on Wikipedia, @brion applied the autopatrol feature to rollbacks (r12126).
I think that basically obsoletes the previous feature. I propose removing the older/secret feature as it seems surprising from a UX perspective that an edit by a vandal is retroactively changed to be as if it came from a bit. It also came up in a refactoring today where it is imho unclear what the expected behaviour is in relation to the patrol system. E.g. if 2 of the 5 rolled back edits are already patrolled by a human, should they still become "bot" edits for consistency? Only some? And more generally — Why? If the reason is only to let patrollers hide reverted edits, then this is already accomplished through "Hide patrolled edits".