Ews here were always caused by ot as well, so it is entirely possible that that is where it is going wrong. My ds is very happy even when massively ot and always has been, and he is about average for sleep, so it doesn't necessarily mean that he is low sleep needs because he can cope. In fact, my dd1 has always been really high sleep needs and the only way we could tell that she was ot was that she found it hard to settle to sleep at night and woke early, so mood isn't always the best indicator.
I would try a couple of days of earlier longer nap and earlier bedtime and see how it works out for him. I do think that he is not sleeping enough, so it is worth trying to see if it helps.
Also worth bearing in mind that there is a lot going on at this stage, developmentally and physically, which can disrupt sleep too. Has he got his 2y molars?