My theory is the Welsh team have developed this trait
into winding up individual opposition players behind the ref's back,
but making sure the ref is looking when the rival team member snaps and retaliates...????????????

Could be, that might explain the number of penalties given against England on Saturday. Or it could just be a failure to understand and follow the rules of the game.
If referees are going to concentrate on a particular aspect of the game (such as high & dangerous tackles) they usually ensure that all teams know at the start of the season in order that they can improve their playing and avoid penalties/cards.