No, it isn't redundant. Steve's saying that with this particular trick, if you don't know it beforehand you don't have a chance of working it out from the level. Not all tricks are like that -- to take a simple example, the blocker trick on Mayhem 20 (assuming that that level is where you saw it for the first time).
I'm not sure about that particular trick of Mayhem 20. I believe there was actually someone who mentioned in the Tehcnical or Game Help forum that they didn't like that trick much, since they found it "cheap" in the sense that it's so different from what the rest of the game has taught you about blockers. In that sense, it's really not too different from the trick in question here. Indeed, one can argue the geoo89 trick here actually is less surprising given the Mayhem 20 trick is already relatively well-known.
And in my e-mail to you weeks ago, I already explained how most tricks and even some glitches can, at least in theory, come about by probing deeper into the game mechanics more precisely, and finding conditions where your current understanding of the game fail to give you a definite prediction, or finding a fine point about the game mechanics that you can recreate using a different, previously unthought of combination of moves. (Though at least for glitches, in practice their discovery often has a serendipital element.)
One might argue though that, perhaps with the Mayhem 20 trick, one is more likely to accidentally stumbled upon the discovery than here, where you specifically have to make a move that, had the trick not work, the move would be completely counterproductive.
On the other hand, surely at least a few of us must have observed that when you attempt to free a blocker by bashing underneath,
you don't always have to remove the entire swath of ground underneath both feet of the blocker in order to free the blocker. This observation can conceivably lead one down logically to a path resulting in discovery of the trick used for geoo89's level.
So, in short, I disagree that the trick cannot be worked out. All the more evident when in fact this level has already been solved by a couple of people as compared with a few other levels, in particular level 10. Certainly compared with something more bizarre like the miner glitch, this is at most a borderline glitch, and hardly defies expectations.