He might really not be able to hold it yet. My 25 month old has been in underwear for 10 months and still wears a pullup to bed at night. Yes, if I wake him up around 11 PM, and again around 4 AM, he will (usually) stay dry, but the way I look at it, he is ONLY 2 years old. It's really no big hassle....he even goes and gets his pullup after batha dn puts it on himself.
On the occasions where we haven't had any pullups due to being broke or staying over someplace or something, I just limited his drinking the last hour before bed, and pottied him at the times mentioned above. But honestly....would you rather toss a wet pullup in the morning/after nap or change pee sheets twice a day?

We are just now getting to where he can stay dry at naptime about 50% of the time. But I'm not ditching the pullups until he goes a whole week dry. I'm 7 months pregnant and I HATE changing sheets.

And, FWIW, I don't think at 2 years old he is really going to "learn" from it. I'm a LOT stricter than a lot of parents on MDC in terms of my expectations but I really don't think it's fair to expect a 2 year old to control what he does when he's asleep.