No, I don't think he was planning to murder someone; however, if he ended up causing someone's death using that thing, he'd still get convicted of murder for it.
As far as premeditation goes, it can happen in the last few seconds before the fatal act is done. It doesn't take much to find premeditation.
Of course he would be convicted of murder using a flamethrower. That is a clear willful act. An act of terrorism, and certainly one of denying Civil rights. He was under no threat, he was the one making the treat.
Just like the ones who attacked the man in the car.....they were the aggressors. They are called antifa/blm. Fascist leftist terrorist.
I see no "premeditation" on the part of the innocent driver...only reacting to the willful terroristic violence of the antifa/blm mob. Personally I , feel he not only acted as a reasonable person would in that environment. But also acted with admirable restraint.