I think it's pretty much what he describes.
If you build your mission in 2-3 minute action sequences, each one escalating from the one before, with a pause or lull in between to reset your emotional state, you can playtest hard on each loop. People talk about BP missions like there was some kind of secret sauce! But most of it was just playing them so much during development.
Loop structure allows players to orient themselves. Players like to have one thing to do at a time. Give them a key objective for each loop, and a complication or wrinkle. Play it a bunch. Is this loop fun? Would it be fun if you came in with low hull? If all your wingmen were dead?
This also creates natural bottlenecks between each loop where the mission space is fairly simple. You can place checkpoints here without much trouble. The player will have a chance to repair or rearm. You can select certain outcomes from the last loop (like a ship's hull integrity, or whether you killed a certain beam) and feed them forward into the next loop. This is surprisingly important.
Say you're building a mission in which two warships duel through a series of close passes. Each pass might be a loop. If, at the end of loop 2, the player has performed badly and the friendly warship is at low hull, you can say, oh, the mission will not be fun from now on, because the player probably cannot save the friendly warship. So we should add a small optional loop in which a transport comes in to fix our friend up.
An exemplar of a long-ass mission built on loops is Delenda Est! I probably don't need to outline the loops in that mission, the rising and falling tension in each loop, and the rising tension across all the loops.
The alternative is the systems/sandbox approach. This is used a lot in BP Act 3, in the Wings of Dawn mission set inside the space colony, in the retail mission 'Into the Lion's Den'. Here, the player is given a set of systems and a set of goals, and their task is to learn the systems well enough to complete the goals. This is a much harder type of mission to design and playtest, and a much harder type to make satisfying for the player.