Sikhs (and Hindus) have pretty much integrated fully into our country - they ask for no extra favours and pretty much get on with life without the perceived chip on their shoulder.
Muslims on the other hand have a real problem with their PR - most of the media report them as not having integrated and demanding special rights.
The Sikhs are therefore trying to disassociate themselves from the Muslims, explaining that just because they are Asian, does not mean that they are Muslim.
It would be the equivalent of you going on holiday to Thailand and everyone thinking that you are French. I am sure that you would try and explain that you don't stink of garlic or have a superior smirk on your face ;-)