Very strange question regarding spit up

My son has had some spit up problems. But he has been pretty good for awhile. Now, after eating eggs, his spit up (looked more like throw up) smells like popcorn

Its strange, but I am not sure if this means he is having a reaction to it or not. Its not even the spitting up part that makes me think a reaction, its the smell....does this sound right to anyone?