There are only a couple of thousand there it appears but I guess the 16,000 number is the paying attendance.
That is correct - paid attendance - official count was 16,316 but I doubt there were half that many there. In fact the Nats have the fourth-lowest per-fixture attendance in MLB (20,690), trailing only Cleveland, Tampa Bay and Florida - along with the Nats' slow start this year, this weather must really be killing walk-up sales.
I was there for the first five innings myself - it was actually pretty comfortable in my section (311) but the winds could be a bit nasty in the concourse and going to/from the Metro station.