Jets need cap space, they are willing to give away Perrault. Certainly the Jets aren't taking on more cap.

Is this a joke?

I agree but I guess the thought from this ACGM is that it's pretty much equal in terms of dollars and the Devils have RHD that are ahead of Vatanen on the depth chart while the Jets could use some help on defense. It makes some sense for both sides but I'm thinking the Devils would prefer to keep Vatanen even as their 'own rental' just for the depth he'd provide should one of Subban or Severson get injured.

I bet there's a lot of teams that are willing to give away decent players right now but quite literally there's almost no teams with significant enough cap space to take them or that would want them.