The use of "we" in place of "you" is common, sort of. It indicates that you are talking to someone that is making a mistake but you can´t point this out, then you, using some tact say ''we".
In this particular case it means that the guy has some kind of police power, so you are carefully handling things. You don´t want the guy think you are patronizing him, saying to him what he have to do.http://life-after-joining-ishayoga.blog ... -of-i.html
Anyway, in other circumstances there will be a reverse effect, the so-called "patronizing we" (usually it goes along a certain "way" of speaking (intonation).http://en.wikipedia.org/wiki/We