I don't know why you're attributing it to delirium. I could very feasibly see someone in a manic state think that setting their clothes on fire would be a fun little prank or something like that. Mania can involve lots of things, from intense anger to intense euphoria, and in either state your decision making skills are severely impaired.

You kind of said it, but mania is a spectrum and hypomanic episodes won't look like this. Full mania might.