Maguire may be the official captain, but Bruno is the de-facto captain. You know full well that he's the most opinionated in the locker-room, has an incredibly drive and is always talking on the pitch. Doesn't mind critiquing players mid-game, or directing them with the ball. He's captain material. It's inevitable that he gets the armband.
Until he's actually made captain we'll get retaliation like the one we seen when he had a go at Lindelof vs Sevilla though. He has to be given it.