Bedrockgames
I post in the voice of Christopher Walken
Interesting. Though not sure I really grasp the distinction there.
I might be quibbling. And this is just my point of view from my little corner of the hobby (which might not align with what other sandbox GMs will tell you). But a sandbox is all about giving players freedom to explore wherever. There isn't an adventure planned for that night. There can be, but the players are always free to ignore it or strike out in whatever direction they want. A situational scenario is planned. You have a scenario set up, but you don't plan out anything beyond the initial set up. So you could have a sequence of monsters of the week or missions of the week all done as situational. But in my view that format ports well into a sandbox (and I think a lot of GMs were always doing this in a sandbox anyways). Or to point to Feast of Goblyns, where they have the concept of a 'wandering major encounter' where the NPCs are expected to plot, move and act in accordance with their goals and in response to player actions. That was a very structured 90s adventure. It had moments that were supposed to happen. But it also had this more free side of treating NPCs and PCs as chemicals reacting together. In a way situational adventures are closer to the language @pemerton is using in that it is very much about the GMs reaction to what the players do (except I would say the action and reaction is much more broad stroke than focused on the back and forth of the conversation)