My nephew's elementary school was nut free...the whole building. And even then, his teacher had a pen, the nurse had a pen, and the main office as well. I honestly cannot imagine that my sister ever let him out of her sight...I didn't really "get it" until I became a Mom. He didn't go to a movie theater until he was 6 or 7, and even then she brought a giant sheet and covered the chairs they sat in and the floor too. Now that he is older he is 100% capable and aware (he is 12)...but prior to that, like when he was a preschooler? OMG I would have been a wreck every day!
It seems to me in my limited experience that people who *have* food allergies are the ones who are aware and ask questions. At dd's open house before school started, a mom asked if there were any allergies in the class, and I know now it is because she has a lethal allergy to shellfish. I don't think it's something the average person thinks about unitl it touches their life in some way.
Because of my nephew, (and the fact that dd had a milk allergy as an infant) I didn't offer dd peanut butter until she was almost 3, so she could talk to me and tell me if she was feeling odd. Had benadryl at the ready and had phoned the doc first. I was so scared, but she was fine with it.
Everyone in my nephew's life was instructed on how to use the pen....so crazy that a Mom wouldn't give you a tutorial.