It looks like the SJ7 has vent holes on top. That's good for getting rid of heat but, depending on what's directly below, it might let dust into the camera. Maybe a metal heat sink is directly below the vent holes and sealed off from the camera interior? And as another poster said, a metal case could be very hot to handle if it's been sitting in the sun on a hot day.
I've never had a problem with my SJ4000 overheating after a year-and-a-half of use, nor has there been any distortion of the case or swelling of the battery. This despite the fact that I use it as a dash cam in Georgia, USA, where we had many days of 38C+ heat last summer, the inside of my truck gets blistering hot, and I've always used it with the battery while connected to a 12V adapter. One hopes the SJ7 will continue to record, day after day, month after month, in such conditions.