Why would someone ask another for forgiveness knowing they didn't do anything wrong?

better to make peace than to "be right"

Perhaps they are a peace-maker, and this seems like the way to achieve that.

Or perhaps they feel guilty about some other past offense, and this seems like it is easier to bridge the emotional gap between you and them.

Or perhaps they simply perpetually feel guilty, about everything or anything.

Or, lastly, perhaps they are North Korean spies, out to get you to divulge state secrets.

To diplomatically stop an argument. Someone has to be the bigger man A friendship is more important than always being right.

Perhaps because they unwittingly forgot Sage when they made the pizza and served the beer?