Van Persie struck the equaliser for United in yesterday's 1-1 draw.
"I don't think he scored, he scored a penalty!" laughed Wenger.
"It counts, but it is not completely the same. When you buy a goalscorer you look always how many goals he scored on penalties, how many he scored in open play. But he took his penalty very well. I knew when he decided to take the penalty that there was an 80 per cent chance that he would score. He was our penalty taker and I know that he does that very well, he does a lot of things very well, Robin van Persie."