There's way too many plausible scenarios to really think one thing or the other.

a) It never happened and it's just a wild rumour made up by some idiot. I know that Floyd is very private about his sparring sessions (no cameras, ect) so I have to wonder how many people were around to see it that would be willing to leak that information.

b) It never happened and it's a rumour fabricated by Floyd's camp to fuck with Manny, or maybe plant an idea in their heads to go for the body more and walk into some kind of tactical trap Floyd has laid out for him.

c) It sorta happened, maybe Floyd was off balance and slipped or some other innocuous thing, and somebody blew it out of proportion.

d) It did happen and Judah is being a good soldier/friend and covering for Floyd.

All options are equally plausible so it's hard to lean one way or the other.