Footballers aren't dumb in raw terms, they're probably above average. At the highest level the sport requires exceptional cognitive traits.
It's just that the cognitive ability doesn't translate to other forms of thought inherently. My go-to example is usually Cesc. The guy had a brain like a supercomputer—with some of his legendary through-balls he can only be solving the equivalent of a three-body problem in astronomy, but off the cuff in a split second.
But the "Barca DNA" saga and the subsequent movements in his career showed Cesc to be a late bloomer understanding human issues and the incentives of people around him.
With this reporting on Bellerin, what I recognise is a bright young lad who's doing the literary fiction analogue of being a "Pitchfork guy" … he's flipping through strongly reviewed recent publications in literary fiction with a few peers in a reading group. That's a worthy self-developmental hobby. Let's see if he ever has anything to say about literature before we call it intelligence …