Hmmm, I agree with alarkaspree. Keep doing what you are doing as he is clearly getting there. There are very good signs he is nearly there so whatever you have been doing works.
Just relax though, remember there is no definite time to train. It could be another few weeks or maybe another 6 weeks before he stays dry at nursery.
Put him back in normal nappies at nursery for now but whip it off (or do whatever it was you were doing) at home. This won't confuse him. You are just working on what he knows for now. Nursery was just too much today.
I just started taking DS's nappy off at home when he was just under 2.
It was all gradual, he wet himself and I said, "never mind, next time in the potty".
He then started making it to the potty for a wee so that's what we did at home. I just put nappies on when I left the house.
A few days after I was sure he was making the potty everytime I put pants on him and of course he felt the material and just thought, ah, a nappy, I can pee! He then had to get used to the difference between nappies and pants and he knew he was wet and I explained to him to quickly get mummy to help with his pants. This bit was trickier and took a good few weeks so again, I only put pants on him in the house then he understood if we were out it would be a nappy.
We then hit the Poo problem. He'd refuse to do it in the potty and waited until I put a nappy on so we then crossed that bridge with Daddy taking him to the loo whilst he was pooing and showing him how proud he was of his big poo's 
!! Yes, thats right, my DH's poo's!
After about a month I found the courage to take him out in the car a short distance to John Lewis just to pick up something and home again in pants. I just arrived and took him straight to the loo with his portable potty when we arrived and that was enough. Then he was able to go in pants everywhere after that.
That was a bloody boring long story but the point Im trying to make is that there is quite alot of stages to potty training that can take some time with kids and don't panic that he wee'd himself alot today. It was either the pants making him feel secure enough to pee or the nursery bneing too much today but just put a nappy on him there until he has really mastered it completely at home. Good luck