Overheating gets to be a issue in small body large sensor cameras, particularly when in live view or in a mirrorless camera turned on for long periods like doing video. Carrying heat away is a issue and since the sensor is active full time, its always generating heat. IBIS would make it even more difficult. So when in a hot vehicle as in this case, or if the sun is directly on the camera as shown in this case, and the air is hot, its going to limit the amount of time before it overheats. Its not a question of if, but of when.
DSLR's don't have the issue with stills, but when doing video or live view, they also overheat in extreme conditions.
The "R" is not marketed for use in extreme environments, it is not a substitute for a 5 series, much less a 1 series which would normally be the choice to use in this situation.
Just the same, Canon probably wants to have a look at the camera and see if it has and issues that a repair would fix. There are warning icons that are displayed in the event of overheat, the only thing to do is to let the camera cool down.
