Should I be angry or laugh?

I put Dom down for a nap at 1 pm today. 2 pm rolls around and he's still up. So, I go into his room and he has his foot up in the air because I forgot to remove his slippers. So I took them off. 30 min later he's still talking, so I go down again, counting to 10 all the way, and he's banging his sippy cup on the wall (that's how he lets me know his cup is empty) to get my attention. I was angry but didn't react. Now he's asleep!
Where did he learn to be so particular? I've taught him to keep things in order, but he's the one who likes things that way. He's always loved his routines and it just makes me wonder.
What does it mean when you child won't take their nap because their slippers are still on or they are missing one of their stuffed animals or their sippy cup is empty?
It's a little frustrating sometimes because he's not being bad he just has to have things a certain way and it drives me nuts!!!