Then I wouldn't care because I would be learning instead of getting trolled.
I graciously accept advice/information, but trolling is unacceptable in my view.
Alright. First: my qualifications. I studied degree level Chemistry, which covers the interactions of matter and energy, and chemical changes they undergo. That places fire right in my domain. Additionally, I also had to study quantum mechanics as part of the course (along with many other things).

How do you know the thing that sets things on fire is in the physical plane?
A fire is what happens when a fuel combusts in the presence of an oxidiser. These various reactions are extensively studied through a variety of techniques.

Every single chemical reaction involves the transfer of energy, a physical phenomenon, which is measurable. Even if the source if the energy is unknown, it is possible to detect, and it would be trivial to design an experiment to do this. It's also nonsensical to suggest that a physical phenomenon is a result of stuff 'not on the physical plane' (whatever the hell that means).

For Pyrokinesis to be possible, it would have to involve the energy transfer from the mind to an external object. Regardless of the mechanism, this would be easy to observe.