Help my baby rabbit may gave diarrhea!!!!!!?

Got a mini lop buck a couple of days ago. He was just two days off from being 8 weeks (got him on fridAy he was exactly 8 weeks on the Sunday) please don't say it was irresponsible of me because the guy that had him and his mum said he needed him out asap and that's ad the lo vest I could push it. He's been fine eating fine (same pallets he was weaned on) drinking fine, very energetic. Not long ago I think her may of had diarhea because his bum is dirty and smelly but thing is I'm not sure if it's diarhea or if it's because his water dish got pushed to a corner and when i saw it there wAs lots of mushy poo in it. Could maybe not be diarhea and he just sat in the water when he pooped causing it to get sticky and stick on him? I took him for a run and he is still energetic and happy. If after ive washed him and his symptoms persist I will tak him to the vet.