Q:

Post revision shows a different user edited the answer

I've just stumbled across this answer, which shows Jeff as the last editor, 

But, when I view the revision history it displays deceze as the editor. 

So, who's the real editor here? ( Is this a bug?) 

A:

It's unlikely to be a bug... it's probably Jeff hacking the DB in the early days of SO.  I'd guess that he deleted a revision from the PostHistory table but didn't backfill the change to the denormalised version in the Posts table that's (probably) used to render the question page. 
Data. SE (probably) confirms this hypothesis.  The LastEditorUserId in the Posts table is Jeff; but the only edit in the PostHistory table is deceze's. 
I'd only call this a bug in that there's nothing to confirm consistency between the data that states the official truth and the data that's been denormalised for display.  Whether you want this is a balance between determining the likelihood of data being incorrect vs. the loss of service if it is vs. the amount of system resources necessary to ensure the denormalised data is correct.  My checks run daily :-).