The same could be said of non-
freaks 
who have long dangly necklaces also, would it not? Yet you don't hear of 'little old lady with long necklace' being refused to get on the bus. What about people who wear scarves around their necks, or cravats for that matter?
This is all about these two standing out from the crowd, nothing more.
Were Arriva to be that safety concious then they ought to ban people with hand luggage from buses too; driver has to break hard, loose bags fly forwards and injure passengers...
It's laughable and the only reason bussie is being a jobsworth is probably because the staff got a lecture from the company H&S bod, telling them it would be 'more than their job's worth' if they did or did not do something that caused the company to be liable for costs or whatever.
Pure stupidity.