Sometimes bows just break! It always sucks when they do break, but it happens.
I hate it when folks try to pass blame with lame excuses. He could have just told you he was sorry that that happened and that you were out of warranty and there was nothing he could do. He did not have to make up some half baked reason to try to shift the blame on you!
I too live and hunt in the 100+ degree temps in TX, and although I have had a couple bows break over the years, it has had nothing to do with being in the sun!
Bisch