I mean, as the audience, we know that the fifty year old man is just lonely, and has no nefarious purposes in befriending this preteen boy.
But as a parent, would you be able to trust a complete stranger - an adult, an old man, even - who is both regularly messaging and has already had a couple of real life meetups with your kid?
Unless this goes in a completely different direction, and the dad is upset simply because the kid is invested in his gaming, my first reaction is "The dad found out his boy, a literal child, has had meetings with an adult that nobody else knows."