Weirdly, the painting is pretty accurate. This is because, according to the artist, this particular body part is simply more skilled than the rest. Like, MFA-level skilled. "I have my penis in one hand and the canvas in the other," he explained. "I have a very skilled penis, art-wise."
I don't think it's 100% penis work because it would be impossible to paint all the joints. You need extra small paintbrush for that and a penis head is round and way bigger.