Yeah, so I think there's a "thing that's different" beyond what I posted previously that extends play to find out. I was reflecting yesterday on that while you're absolutely correct - the "dont steer the game towards outcomes/events and be curious" is doable and a strident feature of most sandbox play,
Looking at that specific section (Create an atmosphere of enquiry) I'm not seeing anything that isn't widely applicable. To me, it's simply saying when a question arises, let the results fall as they may. All of the questions listed are ones that I would seem entirely reasonable whether I'm running Blades, Mythras, D&D, Rolemaster or anything else.
To me, the key point is summarised in the last sentence:
Don't decide outcomes ahead of time and manipulate play to bring them about.
To me, that is completely aligned with everything Rob is saying about how he runs his games, and is the kind of thing I'm usually looking for in my games.
but it's the and play to find out the answer to specific questions that might be different eg: the examples on p194 under "Create an atmosphere of inquiry at the table." Ask questions about the state of play, and explore them, and then "Be a curious explorer of the game in play" to dig in to the character's as well.
There's more stuff under Actions and Principles that take "Play to find out" and add some extra meat beyond the core - because they're what you do in the game to achieve the core Goals.
To my mind, this section here isn't about playing to find out at all. Asking the player, "Does your character
really mean what they said or is this just an attempt at manipulation?" isn't playing to find out, it's asking a question of the player about their character's intent (it's also something that I might ask in any game, not just Blades, because it's fairly important as GM to understand that intent).
Harper goes on to say that these questions "often lead to goals, approaches and rolls," which suggests they can result in some playing so we can find out. But equally, they might not, or the ongoing play might have occurred whether the question was asked or not.
I can fully get on board with someone saying, "Blades has a very specific processes such that, when you are playing to find out, certain things are encouraged and events are guided in particular directions by the mechanical structures (mostly, towards high-paced action and crazy hijinks and away from extended amounts of plotting, planning and preparing).
I can also accept that some people read the surrounding details of Blades -- processes that are used and encouraged -- and consider some of them part of a wider philosophy on playing to find out. This seems to be the position you're coming from. At a guess, I'd say it's a result of a wider, pre-existing grounding in the concepts behind PbtA, as opposed to coming in blind and reading Blades without any outside advice or assistance (beyond watching two or three of Harper's sessions).
But I stand by my original assertion that
core principle of "Play To Find Out" is not particular novel and is not what makes Blades stand out from other games I play. Many of the actual
processes of play that I engage in when I Play to Find Out in Blades are different to the
processes of play that I'm likely to engage in with a RM or Mythras, but the underlying concept of play to find out remains the same.