Hello and welcome. If you recently got him I assume he's still a baby/very young? Wet tail is very serious and he would be very unwell - it's an emergency really. They can get diarrhoea which isn't wet tail and it sounds more like that. Although the blood sounds concerning.
One thing that can trigger wet tail with a new hamster is stress - they've had the stress of moving to a new home - so it's important to avoid stress while they're settling in. This usually means - no cage cleaning for the first two weeks and no swapping things and changing things in his cage. Then mainly spot cleaning for a while and doing less frequent substrate changes. The main thing is don't do full big clean outs where you clean everything, as this removes all their scent which really stresses them. "Partial" cleans and spot cleaning is better
Aside from that, long haired syrians can get messy bottoms! Poop getting caught in the fur. As rainbow says it might be better to limit the veg until he's used to it though. Ideally don't give any more than a 1cm cubed sized piece (eg cucumber or carrot) and initially only a couple of times a week - then maybe 3 times a week and after 2 or 3 weeks you can give it daily. But they really don't eat huge amounts so a tiny amount like that is fine.
I'm a bit concerned by the blood though as that sounds more serious. If it occurs again I would definitely take him to the vets. But if it seemed to be a one off and he seems fit and well in himself, and eating and drinking normally, then maybe just keep an eye on him.
Any sign of blood with a hamster is abnormal and concerning. Sometimes it can turn out to be from an injury though - eg if they caught themselves on something in the cage. Sometimes it can be a uti and maybe just get into the poop area.
