What the heck? That's about the oddest explanation I've ever heard. What possible landing restriction could that have been? Bigger planes can land in higher crosswinds and, unless extremely contaminated, all JFK runways can comfortably land a 757-200 (the shortest runway is twice the landing distance required with no contamination).. so you can't even say that they shut down some runways and Delta couldn't get a landing slot. I don't want to say the Twitter folks are wrong... but can someone come up with a plausible justification here?