I just tried this, and I don't think it is a cancel. You are just recovering and using Fortress.
You're right, I just tested this out on battlefield and you can just walk around when you land on the platform. However, I think this is actually better for that reason because it means on platforms you can full-hop airdodge into standing options as well as specials and there's only a brief window of vulnerability between both actions, It may not be something that will be used very often, but I could see this coming into play for mind games. In short, I think this is a pretty good find that has some potential.
Edit: Just to be extra sure I did another test, on Delfino during the initial transformation, the platform is a bit higher than the ones on battlefield so you have to use the airdodge cancel on that one. It might be good for someone to look into how this works with other platforms as well. Also, while testing this out, I found out that it's possible to air dodge cancel from the ledge onto the stage, I tested this on four different stages. They were F.D, Halberd, Delfino, and Battlefield. It worked on all of them but it was the hardest to do on battlefield, I think it's because of how the ledge is shaped, but it's doable.
The timing is
incredibly strict, especially on battlefield. You want to do a ledge drop, then perform an airdodge jump while holding towards the stage as soon as possible. On all the stages that weren't battlefield, I was able to use down for the ledge drop, and it felt like I had a marginally better window to perform my inputs. On battlefield, It only worked if I used back for the ledge drop, and you pretty much have to press all the inputs as soon as possible with absolutely no delays then start buffering out the special you want to come out. It's incredibly tricky, and it might take a few tries before it'll actually work but it is doable.
The main concern I see is viability, this seems like a pretty strong tool, but it's really difficult to perform, is the reward worth the execution? I see a great potential for mix-ups here, and it might open up a few punish opportunities that we didn't have before, but I guess the only way to know for sure is to try it out. I imagine this means that some other characters can cancel from the ledge too, but it's not something a fortress or bit of fire can't handle.
Edit: I just did a bit more testing, I've confirmed that it's possible to airdodge from the ledge onto the stage with no lag at all and no need to do any canceling. Meaning it's possible to to airdodge into standing options, needless to say, this takes very precise timing, but it's certainly doable. By the way, so far I've only been able t do this on battlefield for some reason, both Omega and normal. I'll test it out on other stages to make sure it's not just a weird glitch or something.