You misread. A course is 40h (20 classes), and it takes 10 courses to get reasonably conversational. i.e. 400h of class-time (not counting homework, study, and practice in the wild time)
I read the after 10 as referring to the number of classes. 400h seems a little more reasonable, albeit a lot lower than the usual estimate which has it over 1000h
How on earth are you expected to be "reasonably conversational" after 10 classes (20h) worth of Mandarin?
It's just impossible.