R.W.
Definitely sounds like an allergic reaction...probably to the PB. My youngest gets eye swelling and redness from milk protein. He does have a confirmed dairy allergy.
I recommend getting him tested because subsequent exposures to whatever caused the first reaction can be much more serious. I have a great allergist if you are interested..just email me.
Two out of my three children have food allergies...both require we carry epi pens. My oldest is allergic to peanuts and nuts (peanuts are not nuts...just fyi). We discovered this when she was 2 and touched a nut. Put her hands on lips and broke out in hives and started to cough.
Good luck!