It seems odd that someone would not know the copy/paste keyboard shortcuts, but the most likely explanation is that he hadn't figured out that it's Command+C rather than Ctrl+C on the mac.

That being said, while using the 'edit' menu to copy/paste is clumsy, I don't see that it would actually have a significant effect on someone's productivity. So I would not go so far as to say that someone was incompetent just because they did that.