Oh, no, how sad! I'm so sorry!

No. It wasn't your fault. You did the best you could, his past life was just too much for his body to handle. Sometimes when an animal is starved, it weakens their organs and that causes organ failure later on. Or weakens them to the point that an infection can take over so quickly.

I hope you can find some peace that you did all you could and gave him a good life, much better than what he had before. Take care of yourself