I agree with the NA translation, but! I definitely understand how there might have been some confusion!

Originally Mickey does not say “my dream room,” he says “this dream room,” which is very important.

Seeing the word "this" (この) might have led a few translators to think, "'this room' is the room in Ramshackle, so Mickey must be describing what he saw in Ramshackle."

Much like English, Japanese differentiates between things close to/belonging to you (this, この) vs. things close/belonging to other people (that, その), but unlike English the difference is a little stricter.

Mickey uses この for "this room," which can only mean the room where he is. If he had meant the player's room, he would have said その, for "that room."

Since English can be more flexible with "this" and "that," it is possible that people saw "this room" in Japanese and interpreted it as what "this room" means to the player, not what it means to Mickey.

From a Japanese-language perspective, however, "this room" is the one occupied by the speaker (Mickey), not the one occupied by the listener (the player).

(There is no hidden meaning in Mickey originally saying "this room" instead of "my room" and, in fact, it would have been more confusing if he'd said "my room" in Japanese, as we don't have confirmation that he is communicating with us from his bedroom at all. It could have been interpreted as he saw the boy in a yet another room, different from where he is now. His original line is possibly specifying "this room" in order to avoid that confusion.

In fact in his original lines he says there is a sofa in the room, changed to chair on NA...hadn't thought anything of it at the time, but it's possible that

1) JP was mistaken and it was meant to be a chair, corrected for NA

or

2) Mickey isn't actually in his bedroom. He is somewhere else, but NA wanted to rewrite him as being in his bedroom where a sofa normally wouldn't be, so it was changed to "chair" to fit the new, NA-exclusive narrative. Very interesting, either way!)

The idea that the boy was in the player’s room is further debunked by Mickey’s follow-up line when he says that he wishes the player could come to see him on "this side" (こっち側, with "this" being from the speaker's (Mickey's) perspective, while the listener's side (Ramshackle) would be そっち側), too (も in Japanese), just like the boy with silver hair!