Following this approach, we could simply say that 90% of the games labeled as sandbox aren’t actually sandbox.I understand what you mean, but I think the term used is incorrect. Because when I hear the word 'sandbox,' I immediately think of Minecraft. They gave a play area and basically said do whatever you want. However, your game is naturally not like this. I think we should find a different term. Frankly, if a game doesn't offers a lot of mechanics and doesn't say to the player 'do whatever you want, the main story? you don't have to touch it if you don't want to,' then it shouldn't be labeled as a 'sandbox' game. Of course, this is my opinion.
I believe that, over time, this tag started being used to label games that had the feature I mentioned. However, nowadays, they're tagging any type of free-roaming action as sandbox. If we follow this path, a VN will eventually be reduced to just click actions to move to the next image, and soon everything could be considered a kinetic novel.
By the way, I agree with what you said, actually an ongoing discussion about restructuring these tags. This should happen soon, so the terms are likely to change. https://f95zone.to/threads/new-tag-discussion.168425/