I meant that saying someone is stupid is unnecessarily more insulting than saying someone is not intelligent.
The fact that you used that example suggests that in an equivalent example to what Abba_s said, you would not seem correct, so you exaggerated.
It was l’toeles, because his explanation was more reasonable than yours.
When someone has commitment issues, they are not dating for marriage purposes, although they often think they are. Perhaps Abba_s should have made that more clear, as well as making it more clear that he was speculating. Personally, I think it was obvious, and his statement was not motzi shem ra.