My sons did the same even had a little bit of discharge, all my doc did was prescribe a cream to dry out the belly button. No big deal for him but it was scary.
My sons looked "strange" to me, it was spotting a little bit of blood, and just looked infected to me, and it had a smell to it, nothing terrible, but it smelled funny, and I took him in and he had no infection at all, I think it's normal for it to smell some, but of course it could indicate infection so get it checked!