He did seem to say what "SStrikerR" suggests in his post above. I don't know for sure. Most replays edit out the juicy bits of players swearing. So puritanical.
I don't know whether it was a subtle pause after the ball hit the line, or if it was Murray stopping his service motion on the first serve of that point (he faulted when he did end up serving, so the point was played from a 2nd point anyway).
I think it was more out of frustration and competitiveness than a specific thing Murray had done.
Anyway, there are already several threads on this, but i don't blame you for starting this one as those don't discuss the incident, rather they deteriorate into fanboism.
Disclaimer: I'm NOT a coach...
Real tennis: https://www.youtube.com/watch?v=yDqnkLJ9BtM