Still, maybe don't be so judgemental about it. It's very plausible that this could be a completely accidental fire.

• Someone leaves a water bottle sitting on the bench in the sun, it refracts the sunlight into a point and ignites the wood, and this is how much it burned before somebody noticed and put it out.

• Someone's cell phone battery was overheating and puffing up, and they put it down on the bench just to get it out of their pocket, but then it went into full thermal runaway and caught fire, and this is how much wood it burned away before someone managed to knock it down onto the pavement instead (there appear to be scorch marks on the pavement below, which might support this theory).

• Someone was hosting some event at the park, and they ran an extension cord across the bench. But then they overloaded the cord and there was a weak joint here that started a brief electrical fire.