Have you asked him why these things make him sad? And I don't mean a straight one word answer but a full conversation? Is it possible it's transference? Is there anything else that could be bothering him but he is unable to fully vocalise?

I only say this because I was very guilty of this as a child. I would burst into tears over something that seemed trivial to everyone else but it was usually compounded by a bad day, something that had played on my mind that I couldn't say or tiredness. My daughter is like this. And it's taken us a while to work backwards so she can see it too. And she is 12. She told me once she cries on the inside but sometimes it falls out. That sounds way more awful than it is. But we've been able to work on it. I don't think she is suffering. But she is very empathetic. She used to worry about being upset about things and telling us in case they upset us too. Apparently that's common for kids who have a high EQ. It's still a work in progress.

My DS is the opposite, very dramatic and very open with how he feels. Not a bottler, and when he does bottle it manifests physically almost immediately.

Sorry for rambling, it's just something we've worked on for a long time and this is exactly how it produced itself, although a little younger for us.