Originally Posted by xliioper

Was your IAD - ATL flight on the same ticket? The Skyteam access rules (which would apply since it's not a DL Sky Club) make clear that if you are on international Skyteam Business and connecting on domestic or international onward flight you are entitled to access.

"Lounge access will be provided only at your departure airport and not on arrival, unless you are connecting to a domestic flight or other qualifying international flight."

So the only excuse I could see is if they weren't aware of the IAD-ATL onward flight. DL Sky Club access rules are somewhat different and do not require connecting onward flight from international J. But those rules wouldn't apply since it's not a Sky Club.