Yes, but what food from McDonald's? And which particular ingredient? Take a
look at their standard ingredients list (if it's not posted, ask for it) to
see if there's something out of the ordinary.

There's some chance that part of the reaction is a real food allergy and
the other part is resultant panic. It's hard to tell where one leaves off
and the other kicks in. With reactions that intense, though, he should see
a doctor, preferably during such an attach.