Tellers for established political parties are carefully briefed about what is and is not allowed outside a polling station. For instance you may wear a coloured rosette, but not one with the name of a candidate, and you must under no circumstances try to influence anyone.
The so-called "Brexit Party" is not an established political party. It is a private company with a tiny number of actual members, although they recruited a lot of supporters and took their money without allowing them to become members with a say in anything. I think it is quite likely that some of these supporters acted as tellers yesterday without understanding the rules.