His version. His reaction. This isn’t an instance of two different musicians covering the same song with some coincidental similarites — Coulton’s version introduced a lot of variations from the original, and Glee’s copied every single one, note for note, word for word.
And it’s not like they ripped off someone nobody likes, like Intellectual Ventures or Todd Akin. This is Jonathan Coulton. He’s one of the most beloved geeks on the internet. It would have been safer to rip off Mother Teresa.