Fiasco with the truck brakes today. Grrrr.

I do towing and service for a living. I get 2 or 3 tow jobs a year because of caliper bolts going bye bye. It seems I often see it on the front wheel of GM front drive cars. If the trailing bolt comes out, as brakes are applied the caliper tends to pivot off of the leading bolt, which causes caliper to scrape along inner surface of the drop center of the rim. Depending on the rim design, it may be a smooth surface or have ridges corresponding to the spokes of the rim face that abruptly snag the caliper and lock the wheel. That is probably how the crack happened.
Get home safely.