This is par for the course with exercise science. It's mostly fake. No blinding, small sample sizes, researchers with agenda, low duration, low funding etc. The good news is that doing almost anything works.
You're right, it's impossible to blind subjects. Researchers can be blinded by having one limb be the control and the other be the test. This design has become more popular recently and it's definitely a small improvement.
Progress, over time, tends to involve both variation in routine and specific methods, progression, programming, modalities, techniques, form, movements, etc.
One somewhat dubious 10 week study of newbies, as many others have commented, doesn't communicate much.
A further complication is that much of the hypertrophic adaptation is systemic, that is, relates to overall body stimulus and other factors (nutrition, rest, genetics, etc.). Among those effects is the net hormonal response (testosterone, HGH, ILG
Heck, there's a well-known phenomenon called cross education* where an untrained limb will see strength / hypertrophy gains when its opposite is trained:
