[alibarber]

It's probably much more boring. The choice was likely between leaving the whole water bottle and its contents in a bin of forbidden/discarded items, going home and missing the flight, or chugging it, or arranging a courier for said bottle.

Probably the act of defiance of pouring the contents onto the floor where there was no drain was implied to be disruptive and would have lead to harsher sanction for no reasonable payoff.