Wow- sounds like your little guy was pretty upset by his spill... I can't say for sure what is going on from your description, but I can share what my son's night terrors are like. He's never had them during nap time... from the little research I've done, that would be highly unusual.
Nick's night terrors started at 10 months old. He's never been a great sleeper, he's highly active/spirited and fights sleep- There's too much to learn and see
Typically, his night terrors start 2-4 hours after he falls asleep for the night. he usually has a horrific high pitched screaming cry- it is eerie sounding.
When I go into him, he usually has been sleep walking/crawling in his crib. His eyes are open, but he doesn't respond to me or seem to recognize that I'm there. He'll keep screaming for 2-5 mins no matter what I do.
In contrast, if he has a nightmare, Nick will cling to me and calm down with reassurance/comfort. When he has a night terror, I just stroke his back and repeat "Mama's here, baby, It's okay". Until he's back asleep. My little guy does sleep walk and seems to have major sleep disturbances, but both my DH and I were sleep walkers/talkers and it seems to be inherited.
I don't know if that helps clarify,... but I thought I'd share.
Does your little guy seem to recognize you when you go to him?