I didn't see a source for that, it's been insinuated its for the weight cut then? In that case it's crazy thinking on Bonnar's part...if he pulled off the miracle win then it would have been overturned anyway.
Drostanolone is what bodybuilders use in their cutting phase usually for a few weeks before competition time. It helps get rid of the water your body retains. So when they go on stage they look solid and ripped.