Mark rosewater classifies this as an activity as per his article here
Mark shares his definition for what constitutes a game and explores what you get when one of these aspects is missing.magic.wizards.com
He states, "Games are about obstacles. The players have a goal, but something keeps them from simply accomplishing it. A game needs to have some challenge to it because the fun of a game comes from figuring out how to overcome those challenges."
It's his own definition of course and not one that everyone needs to follow, but I do like that it puts emphasis on requiring some type of obstacle or restriction to be satisfying. And given Maro's pedigree I'm inclined to value his opinions
VERY MINOR SPOILERS FOR TOTK
Of course he's not wrong, the rules make the game, but considering MTG has been driven directly into the ground (not entirely his doing), I wouldn't defer entirely to him. I think Nintendo did a phenomenal job creating an open air world with the Sheikah Slate providing a set of flexible mechanics to contain the world but to me, finding my own solution has diminishing returns compared to discovering curated solutions as I did in previous Zelda games. I haven't gone underground much in TotK yet so maybe they did to try to balance the sandbox with curated, scripted gameplay. That seems like it could be a decent compromise. Looking forward to getting a better feel for the game.