It might not be technically correct that they learned the full set of Chinese grammar in a week, but I can imagine one week is sufficient for a beginner to get the basics and start reading/speaking/writing the language and absorb the other nuances or nitty-gritty details through everyday usage.
I mean, I'm pretty much a Chinese/Cantonese native user, so I can't be sure about that since I never "learned" the language in a classroom setting, but my impression is that this short period of learning grammar for Chinese language leaners is quite typical.
I mean, I'm pretty much a Chinese/Cantonese native user, so I can't be sure about that since I never "learned" the language in a classroom setting, but my impression is that this short period of learning grammar for Chinese language leaners is quite typical.