I’m trying to figure out a ruling for something one of my players wants to do. They’re invisible, but they took a couple of seemingly non-attack actions that my gut says should break inviz.

Specifically, they dumped out a flask of oil, and then used a tinderbox to light it on fire. Using a tinderbox isn’t an attack, nor is emptying a flask, although they are actions , and the result of lighting something on fire both seems like an attack and something that would dispell inviz.

I know that as DM I can rule it however I want, but I’m fairly inexperienced and I don’t wanna go nerfing one of my players tools just because it feels yucky to me personally without understanding the implications.

Is this an attack or is there another justification for breaking inviz that is there some RAW clause I didn’t see? Or should this be allowed?