Dog died at the vet's

A couple weeks ago I noticed our dog Gauge was straining to urinate but couldnt. I read one of the former questions on your site, your answer that it was an emergency and I rushed him to the vet. The vet knocked him out, did X-rays and blood tests. X rays showed that his bladder was so swollen it was making him constipated as well, they didnt see any tumors or stones, blood work showed that there wasnt any infection. Vet said the prostate felt a little big but nothing that concerned him. We left before he woke back up so the vet could insert a catheder and so Gauge could stay the night. The next morning the vet called and said the catheder went in smooth, he didnt feel or sense any obstruction and that later that night, he took Gauge for a walk and he was passing stool on his own. It was then he told me the next morning when his assistant went in she found him dead. I know it doesnt matter anymore but I cant help but be suspicious that the vet might not be telling me the whole story. Because I left before he woke up I thought maybe it was an anesthesia complication. The way the Vet talked to me on the phone he was acting very defensive. kept saying "I dont know what happened" actually, that was the first thing he said to me when I answered with "hello?" like I said I know it doesnt matter much anymore because we had Gauge cremated that afternoon but I figure maybe you could put my mind to rest so that I could feel safer about taking any future pets to him or if you think we should look for a new vet.