Well, the problem here is that there is conflicting witness testimony and reports, credible journalists (e.g Roohan Ahmed) and witnesses are saying a few protestors did it while others say Police so it's hard to determine it based on that (See Afghanistan).
(while writing this i just found a video of a protestor lighting a tree on fire)
My other issue is that there is so much video evidence of trees and shrubbery on fire while protestors are there, one could make the argument that it was because Punjab Police prevented so but i doubt this because i don't think the regular police are good at OpSec and given the frequency of videos coming out, hard to see why there wouldn't be videos of the incidents happening.
Note to others who may reply, i don't see them as representative of all the protestors, they are a few bad apples and are present in every group.
