Regardless my position about breeding. When it comes to your question: Yes. I think the vet screwed up big time. It should be the most basic thing that he could realize she was pregnant before putting her under, let alone cutting her. There should be at least a simple physical examination just to make sure things are good to go and there is not an obvious condition not to go ahead unless the pregnancy was at the very beginning and unnoticeable.
" How we behave toward cats here below determines our status in heaven."
- Robert A. Heinlein