He doesn't sound like he is outside the realm of normal to me. So many kids this age seem to live on fresh air alone, even previously good eaters. So long as you keep offering the variety that you do then I can't see any lasting issues as he gets older, but if you only ever gave him his preferred food, that's when I think a lot of the trouble starts kwim? Plus when they have been sick, they sometimes just don't have an appetite for much.