Are you serious?? He is offended by something so small?
Why not tell him he can believe dogs are smarter if he wants to, but it won't change your mind...
Honestly the intelligence of different animals is so subjective. The only way us humans define intelligence of an animal is by comparing its behavior to ourselves- which isn't exactly fair, in fact it's condescending....
Lol, why not try to have a debate about it

It might spice things up