Hard to imagine if caused by wind, this was the first time for a 20 year old building.
Possible standard vortex shedding excitation combined with degraded foundation would be my guess, if the assertion of no seismic activity is valid.
Other excitation inputs could be vibration from a subway...I've no information about the surrounding town.
But they seriously need to check their foundations. I can't imagine what else could cause this two decades after construction. It's seen all the wind it's going to see, so it has to be something else. And sure, maybe some of the steel is crap and is fracturing or rivets are failing in the walls.
Or, maybe GW Bush's team of Secret Squib Secreters is planning another 9-11? (just kidding)