When my smaller male Boa, Butch did the same thing once, I was puzzled.
He slammed the glass again the next day as I walked by which is just soooo out of character for this sweetheart. Even though he wasn't due for a feed, I fed him anyway. He didn't slam the glass anymore and hasn't acted that way again.
I reckon just like humans, these guys can have sudden cravings for food as well. My adult BP has gone into major feed mode before way before scheduled feedings.
Butch, Wild Type/Common BI