Frosty's Floating D-air?

[the5souls]

Frosty gets knocked back, then he uses his double-jump to recover. Then he tries to d-air, but ends up floating for the entire animation. Commentators think this is intentional, but I have never seen this before. Frosty doesn't even react.

What happened? Can we reproduce this?

Happens around 45 seconds in:

 

[Luigifan18]

Stall-then-fall aerials don't stall or fall if executed to hitstun cancel, as they could be excessively powerful (albeit foolhardy) momentum canceling tools if they did. They've worked like this ever since Brawl.

 

[TeamChevy86]

It's intentional. Happens with Bowser's dair as well. If used at the right (or wrong) time the momentum cancels itself out or something and you go into this weird slow fall