It was only a small group behind the dugout who were shouting it at him.
The whole thing stems from Mourinho and the potshots he's been taking at Chelsea pretty much all season. One minute he's calling us a defensive team, the next minute he's insinuating that we're only top because we have no European football and the next minute he's bemoaning our "luck in front of goal" as in we're lucky because we actually convert the chances we create, as opposed to United who are lucky because they struggle to convert the chances they create. He seems to try his best to go out of his way to belittle our success and discredit the season we're having.
Calling him judas is ridiculous. He's entitled to manage who he likes, but he'd do well to remember what he himself said about Lampard when he signed for City. He said "once you play for a rival team, the love story is over".