Well your assumption is that there was a new line. A second receptionist came on duty and called the next person from the one single long line. Someone from half way along this single line decided to go form a new line by himself behind this 2nd receptionist rather than wait in the single line with everyone else. This is not like a supermarket where it is more or less necessary to have a separate line for each checkout.

Either way, I still feel justified in going to the 2nd receptionist when she looked at the single long line and asked who was next, given that I had been in line before this other guy. Nobody has said I was in the wrong in doing this.

I also 100% realise that I have already gone way overboard on this thread