Well you know it's silly, so I won't rub it in. Heat isn't a factor for a number of reasons. First of all the 40°C swing in ambient temps is small compared to the total swings that rims routinely see from brake heat. Also the rim expands as a ring, with the inner and outer edges each expanding/contraction in proportion to their lengths so there's no relative change. The rim does get longer, so the diameter increases (or the spoke tension rises or both) with an increase in temps, but not toa degree that anybody would ever notice functionally.

I suspect that the reason the rim joint opened the way it did, is that the impact was just off to the side of ir. Buckling that pare downward, and pulling the rim towards the point of impact. (based on the photo).

You won't have the ability to correct this local distortion via normal alignment methods, but a bit of work with a file, and maybe a spot of filler will make it OK. If you're really good at aligning, and have good file skills, this wheel can be made to ride and brake as good as new, but even they it's not something you'd want to start a long tout with.

BTW- since this is a front wheel, normal stresses are fairly low which is good, but you want to be extra diligent about making sure it has smooth even braking action, so there's no surprise grabbing in an emergency stop.