Looks like they found it by platforming. I'm surprised they didn't have an invisible wall to block them from getting to it.

It is in the Corrupted Strike. This is absolutely not the real way to get there but it's the path we used. The real path is quite obvious but right now it's an instant kill volume. All three classes can make this jump though warlocks may have to pop super.

Emphasis mine. It’s a time-gated thing, something Bungie hasn’t flipped the switch on yet. I know Bungie can’t just put all this stuff in the game and let people find it as they will—everything would be found within a week. But time-gates do sort of bother me, especially when they try and play all coy like “you’ll just have to find out.” Which, to be fair, they haven’t done with Malfeasance as far as I’m aware.