No it's the chips, these machines didn't exactly have the most user friendly heat dissipation design, on both models the CPU heat conducted straight through to the top case. maybe not cook an egg very fast but uncomfortable to touch for more than a second... maybe 1 EPH (one egg per hour) :)
Now the old Powerbook 5300's actually did catch fire. My 1st tech job was a hardware technician at an Apple production facility mostly building and refurbishing Powerbooks, can confirm.