In a fairly recent study of LA-area wildfires, 100% of the wildfires were either deliberately human caused, or caused by downed power lines. 

In the most recent year, LAFD also responded to over 21,000 encampment fires. 

I don’t think we should be shocked if it is in fact true that at least one or two of the LA area fires were arson. I don’t even think it’s insane to make it the default assumption, to at least rationally discuss what, if anything, can be done from a policy standpoint to reduce them.