Was Peter even that good a pianist?
When we see him playing at the recital, he's bashing away at the keyboard like it's a drum. It's one of the least tuneful things I've ever heard.
I understand that he was supposed to be distracted by news of Jess' pregnancy, but his playing didn't come across like that. It came across as somebody who flat out couldn't play. Surely he wasn't so distracted that he literally forgot everything he knew?
Maybe he just wasn't that good a pianist to begin with.