Is my pediatrician crazy???

So my son is 4 months old and he went today to get his 2nd round of shots. He asked if he was following our food and interested I told him he was definitely interested and that we had already started him on cereals. He told me to just go ahead and give him what were eating and try foods like peanut butter, fish, eggs just to see if he was allergic to any of it. But I think hes to early for those things he doesnt even have teeth yet. I mean were going to start the supported sitter carrots, greenbeans and sweet potatoes. But that other stuff is just way to early for. Am I overreacting or is he really crazy?