What you posted may be true but there's a reason why this subject is controversial. There are plenty of experts arguing once per week, twice per week, and even three times per week, each with their individual studies. Read the article in this link sponsored by Testosterone Nation.
http://www.t-nation.com/findArticle.do?article=265game2
Christian Thibaudeau says that
for maximum progress, regardless of how many weekly sessions you have for each muscle group, you should do the same weekly training volume. For example, if you do 120 total reps per muscle group per week, you can do either one session of 120 total reps, two sessions of 60 reps, or three sessions of 40 reps. When you add weekly training sessions, don't double or triple total weekly volume. This will lead to stagnation.
So could it be true that the study that you offered is optimal for training 2 x per week but not 1 x per week? However, if you increased the volume of training, it would be optimal for 1 x per week but not 2 x per week?