Updated 15 Apr 2012 to add the note at move 19. Thanks, Richard.
It seems that many players--well, at least some-- who are quick to disparage the Blackmar-Diemer are at the same time prone to go to some lengths to avoid playing into one, although the late GM Larry Evans once wrote that the best way to refute a gambit is to accept it.
However, I can understand this attitude. It makes perfect sense. Why waste time studying defenses when the gambit is so bad? And why take even the marginal chance of suffering the embarrassment, the ignominy, of losing to it?
Consequently, BDG lovers often go to extremes to sneak in a BDG. And others probably slip into one perhaps without even realizing it. I have no way of knowing which was the case with this recent game. I've posted several times earlier about this. After you play through this game you can check those posts here.