Potty Training Question

Did you ever have trouble with your child not understanding that poop doesn't come out of the same place that pee does? And if so, how did you explain that?
My son is almost 2 & 1/2 and we've been working on potty training. He does pretty good with going pee in the potty. He's able to tell us when he needs to & even goes in & does it by himself. But up until today, he hasn't wanted to go poop in the potty. He's always just asked for a diaper. Today, he went in all on his own & tried to go but was having trouble. He would tell us to leave & then a few minutes later he would call us back in & kept pulling at his penis saying "Out poop! Come out!" It was really cute, but the poor baby was so upset! We tried explaining that the poop doesn't come out of there, but all he did was cry. And he didn't want to give up! Finally, we told him how proud we were that he tried, but he needed to take a break and try again later. Any advice??