Husband keeps referring to his last wife as “my wife”

Now this is kinda complicated. My MIL married a man she dating for 2 months then married. Before they met he had a wife of 15 years she passed away 6 months before they met. Me and my husband were talking to him and he was talking about his wife that passed away, he kept referring to her as “my wife”.

I didn’t see any harm really, they never divorced so she wouldn’t be a ex wife and he was with her for many years. Anyways I could see my MIL was getting angry and pulled him into the other room. (Thin walls) we could hear her saying she is his wife and that’s his “ex wife”.

Now i felt her saying that was inappropriate because she passed away and still will always be his wife. Ex wife feels more appropriate if you divorced.

Is it appropriate for him to refer to her as “his wife” or “ex wife”?