IT isn't likely that the shop forgot to refill the coolant, unless that was the very first few minutes that you had the car back from the shop. I'm guessing the radiator was replaced (they would HAVE to refill the coolant or it would've negatively impacted the car already). Otherwise you'd have noticed it before, or the car would have overheated. In other words, there would have been some sort of indication. If it was only 1/2 full, it could've been at normal temp in cooler weather, but once you worked the car out, it heated up too much.

Also, usually shops will run a car for an hour or so after it's been hit in the front, to make sure that it idles right, the fans come on, and it stays cool. It's likely that they did that, at least to some degree.

Possibly, working hard in the snowstorm, caused a big heat buildup. I don't know how bad the snow was, but if it impeded ventilation to the engine compartment, or if there was excessive wheelspin involved, there might have been high levels of heat generated underhood.

Other than that, if there was wiring work done, the current draw from one of the underhood accessories might have been enough to set it off. Additionally, a ground bus might not be well connected and could've caused resistance problems. That is a very easy thing to check when repairing a crash, but it's something that could build corrosion or come undone at a later time. Pinched wires, etc., are all possibilities. Add to all these things, the potential for moisture to enter places under the hood in heavy snow.

These are just some ideas.
--
Chris Herbst, in Wisconsin.