Sleeping baby

So I put E down for nap time without rocking him. Right down in his crib. He moaned (never really crying) for about 30 minutes. I went in and patted his butt and walked back out... and he fell asleep. I wonder if it is a fluke or if I do this during afternoon nap if he will fall asleep on his own. The goal is to be able to put him in bed and he know it is sleepy time and fall asleep on his own (self-sooth as they call it). We will see.