The government was already fighting fires in the area that had been ignited by lightning. There was a no-burn order in effect due to dry conditions. The Hammonds started the fire anyway and it spread out of their control. So yes, I think their actions could well be termed "malicious".
I don’t think so. Where was the “intent” to do harm. The fact that it got out of control is not a deliberate intent. Questionable at least, legally.