Hi,
It's completely normal for kids to go off thier food when they are teething, so please don't worry. I found that soft foods helped DD like yoghurt, cheese, toast, pasta and soft fruits. To be honest while she was teething i gave her what i knew she was going to eat, if she didn't eat her main meal then i wouldn't make a big deal about it and would offer her a yogurt or something else instead. When she stopped teeting she went back to eating normally again.
I think the important thing is just to make sure he is eating something rather then nothing.
HTH:)