He's just not like the many fighters who put on weight after the weigh-in. He's probably generally around that weight range. Maybe he had a big breakfast before weighing in.
You know what Floyd boys are like, their tongues wag so much that they have trouble breathing from the sheer mass of the things, if they didn't eat so much fried chicken:yep they wouldn't be providing their tongues with all that protein.
His weight just fluctuates because he doesn't really dry out. A normal person who isn't mucking about with their weight will gain and lose a pound here or there. You take a **** and lose a pound, you have a meal and gain a pound. Floyd probably ate before the weigh in but didn't eat before the fight and the unofficial weigh in. The only time Floyd did a small dry out was in his last fight or two at 130 where he said he didn't like making the weight anymore because it was too hard... ...AND THAT WAS SIX OR SEVEN POUNDS!
Generally guys will do one of two things. Eat **** or eat good. Hatton likes a full English breakfast the morning of the fight and then he'll get all the carbs and **** in later. DLH for example likes spag, lasagne or some **** like that. Packed with the carbs for energy. Obviously they won't be eating a few hours before the fight. They don't want to feel full, get a stitch etc