I just realized that the study you posted was a 20 week long experiment with the test. dosages. The fact that their diets remained unchanged and were told to not exercise is impressive how much FFM they gained. However, it is still not 100% muscle. The constraints placed on the participants is evidence that while they clearly gained lean muscle, it must also include glycogen and water. It is well known that once a steroid cycle is over, there is weightloss as a result of the excess water being urinated out. It is a long 20-week steroid cycle with the same result once the user ceases the drug.
And your point on the other AAS and their gains being primarily glycogen/water, I fully agree with. Their effect in this regard is much more pronounced then say Testosterone, while also having less of an anabolic effect in comparison.