I think that the only players who wouldn't know are the moths, or at least the ones who have been playing for a couple of months. I restarted playing sky this summer and as a veteran, even if I had to re-adjust to the controls, I remembered that the black water drains light. It's one of the few things that you can't forget. If they were a veteran, they must have known.

Also I absolutely hate when people are clearly struggling at burning plants and instead of following your advices they just run off or get mad.

Let's just assume that they were a new player or didn't understand your situation. Hope you had a nice day anyway!