Couple of things:
1. I think the design is not good. Your neural drive is way higher after leg exercises that most exercises feel easier (potentiation & catecholamines). If you do 3 sets of leg press, leg extension and leg curls, you will be flexing your arms even if the author told them not to. They should have it the other way- arms after legs.
2. The muscle volume is same, but the LA (hormone group) had more CSA! How the heck is that possible? Maybe the muscle got smaller in the distal and proximal regions!!
3. 14% & 21% increase in strength for doing 6 sets of arm curls 2 days per week for 11 weeks is wayy too small for untrained. That means if you use a 20 lb dumbell and just workout legs and arms for 11 weeks, twice a week, at the end of 11 weeks, you could do 25 lbs or less!
4. And as I said before, people are always skeptical of studies coming from the labs who are proponents of the theory. People tend to believe results from other independent labs.