While I also suspect arson, here is a possible explanation for how it CAN be a coincidence.
Imagime you have a nearly uniformly flamible forest. As in ther is roughly the same amount of debris built up everywhere.
Then you get clear skies and a hot sun. Everything heats up uniformly. Until everything reaches spontaneous combustion at the same time.
Not likely, but possible.
NOT POSSIBLE to have multiple fires SPONTANEOUSLY COMBUST AT ONE TIME. DUH
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