I remember having a few friends at that age telling me things that made me uncomfortable, including one who said she was hearing voices. When I talked to my mom, she just blew off; I wish she hadn't, because it just made me more scared.
Turned out, the friend who was hearing voiced was later diagnosed as schizophrenic. Another friend was being abused. The rested of them were just messing with me, wanting attention. My friends with the issues, their parents had no clue at the time, and years later expressed the sentiment that they wished someone had spoken up sooner.
My point is that you can never be sure of what is real and what isn't, and who isn't getting help and who is. It doesn't hurt to speak to somebody who is a position to help, just in case something is wrong. If it turns out to be nothing, so be it, you did due diligence, but if something IS wrong with this kid, maybe you were the one who helped detect it early. If it is already being taken care of you can help your son cope with his feelings around this boy.
And why should he stay away from, as one poster suggested below? Is it just because he's different? Or because he said something off the wall? We need to learn compassion for people who are different from us. Just because he might have mental issues doesn't make him pariah.