If the sun can get at a strung bow, the heat absorbed through the glass can reach a temperature high enough to damage the bow. Very good chance that leaving it strung in the car, even with the windows open, likely not wide open, damaged the bond, which later gave way.
In hot weather, I never leave a strung bow where the sun can get at it for any length of time, even on the bow range while taking a break from shooting.
A couple of years ago, a friend of mine left his strung bow in his tent at the Compton rendezvous. I believe he had the flap open so the sun could hit it, or maybe it just got very hot inside the tent. Regardless, he never got a chance to shoot the bow. The lower limb delaminated inside the tent.
In your case, can't say for sure that's what caused it, but can't say that it didn't, either. Chalk it up to experience.