Could well be ... the problem is though - if "no other photographers" is written into his contract, and another photographer turns up and starts shooting, then the B&G are in breach of contract, and that can have some serious legal implications eg
- The photographer may argue that the other photographer confused the guests to the point where they didn't know which photographer they should be looking at, and as a result the official photographer's reputation was tarnished because he wasn't able to get the expected number of quality shots due to this - or due to the fact that the un-official photographer caused delays.
- The photographer may argue loss of income if the guests choose to receive photos from the un-official photographer (that were taken after the official photographer posed and setup the group).
- The official photographer may even argue that the photos taken by the un-official photographer used his intellectual property (if he poses the group / selects the location / controls the light etc).
- The official photographer may even refuse to shoot.
Personally, I'm about as easy-going as it's possible to be with regards to these kinds of things ... but others aren't necessarily as easy-going. Some will say nothing - some will say something - some will totally spit the dummy.
Personally, I think it's just a courtesy thing.
Photographers are like a box of chocolates ... you never know what you're going to get