Probably it has to do with the "iron bird". The rollout ceremony was carried out with the iron bird in the background. Hopefully, there's another flight testing prototype built in parallel with it.
I have to correct you guys here.
Iron birds refers to flight control and hydraulic system test bench.
all the systems (hydraulic pumps, control electronics , actuators, backup systems, flight control computer etc etc) are built to design specification and mounted on a steel rig. the giant steel rig and the location of these systems are to scale of the actual aircraft, and the control surface hinge moments (air loads on surfaces that actuators has to work against) are computed via test computers and fed into a systems of counter actuators that simulates the actual in flight hinge moments so that the a/c actuators has something to work against.
as such the steel rig that whole flight control system is mounted on is not anywhere near the flight structure.
so it wouldn't be correct say that "another flight test prototype".
in flight test programs, even the structural test articles are numbered, for example such as T1 S2, S3 T4. meaning flight test article 1; structural test article 2; structural test article 3, flight test article 4. so on and so forth.
an Iron bird would not count in that series.
If the Y-20 rollout is indeed a structural article hand over. then,
either
1) that picture is not the Rollout even but an ironbird milestone event. an old picture.
or
2) the structure that handed over is a structural test article not meant for flight but is a full structure setup and the picture is a shot of structual test step up not ironbird. a structural test stand would equally have such beefy structure.
typically when people are building complete structures, IB would be in operations anyways as the the flight controls definition especially the all crucial rear main wing spar definition, where all the tightest fitting of control actuation systems occurs, already be nailed down.
