I'm not actually sure this is a bug, but it certainly was unexpected. I started a Hamlet compatible Don't Starve Vanilla (Not RoG) game (out of curiosity) and was collecting the bits for a Skyworthy when Bearger from RoG spawned at the end of the Fall season. As I said I'm not sure this is intentional or not.
Start a Hamlet Compatible, non RoG game. Wait for the 2nd fall Season.