Yeah, it actually also makes sense for an actor to avoid seeing other films with that character if they're going to portray an entirelly new version of that character.

In Method Acting character building is a lot about what are the motivations and drives of the "person" which is the character and "living truthfully (the character's life) under imaginary circunstances" and judging by how he talks about it he is indeed using Method Acting.

As for games, they might be an even worse influence than previous films because the emotional depth of in game characters is generally zero or close to it (except in things like cutscenes were they used actors, MOCAP and a very detailed model for expressions), akin to a woden performance.

It's valid for an actor using Method Acting not to want to be exposed to a different representation of the world their character is supposed to inhabit and of the characters in that world - Method Acting is pretty "soft and smooshy" rather than a set of iron rules and mechanisms, relying on a person's own "emotional engine" and ability to pretty much forget that they're not that "person" which is the character living those things (think of it as an actor's version of suspension of disbelief) so who knows what influences the actor might take in subconsciously which then affect their embodyment of that character, which would be a bigger concern now that they've already embodied that character (for the last season of the series) and that should not change for actor reasons rather than character reasons (i.e. the character should only change due to things that happen to the character).

No doubt some actors would think that playing the game would make no difference, but it's valid for some to think it might.