I think the emphasis on the "planet" is that in their usual over-ambition, Hello Games announced that they'll be simulating a full-scale planet. It then got through the media's broken telephone.
I mean, we have Pathfinder which spans over an entire Star system and even beyond but still is a fantasy roleplaying game. (Same with Dungeons and Dragons)
They probably specified to emphasize that despite NMS being interstellar, this one isn't. Since they're known for the former, that reputation comes with the baggage of expecting a similar experience.