Hmm, it shouldn't, but...
Well, if I took indirect damage it didn't drop my health below 100% so... idk.
Edit: Bleh, I don't want to test this right now. I'll just go for other badges. The only other thing I can think of that would cause this is that I killed the last Bruiser Brother while he was out of sight with a power modded BFG. Maybe I gibbed him and it didn't count? Who knows.
Edit 2: The only other real difference between my run and MaiZure's is that I never actually completed it. I died on the following floor.