My understanding is the SBCPD employed both smoke and tear gas canisters. These are fired projectiles and have igniters which set the charge off. These projectiles frequently lead to fires when employed against barricaded gunmen in a building with combustible materiel (carpet for instance) around. The technology appears to be pretty old and basically unchanged since the 1930’s.
Again, I don't want anyone to think I'm defending the psychopath that was inside, I just have a real problem with the field guys making decisions to snuff people and getting by with it. It was pretty obvious in this case that they were prepared to offer exactly zero patience in an attempt to wear him out or try to bring him before a judge. The fire was burning as soon as they could get it lit.
And as a side note, I tend to believe the guy was railroaded by his corrupt buddies... as in, his story was most likely true at it's core. I don't trust cops anymore, I've seen too much and I'll go to almost any length to avoid ever having contact with them... I don't even want them knowing my name.