That sounds like some diuretics were used. McClellan used to do someting close to it at the same day, he wouldn't get past modern testing I guess.
There is a limit. Everything beyond 20lbs is a rather difficult task. I´m guessing he re-hydrated 20 something pounds and weighed in again while clothed. Note that muscle carries water really well, and Broner is quite muscular.
James Toney dropped 30 pounds in two weeks leading up to his fight with Roy. Rehydrating 30 pounds is a lot. He may have been using diuretics.
Didn't Gatti one-time gain about 25 lbs in 24 hours and almost killed some poor guy that only gained 5 lbs. (think it was an ESPN type fight)