It's not as if these students are just visiting on holiday and will get by not
using the language of the country they are in. They have come to an English speaking University for a long course of study and I believe it is the hight of rudeness if you intend to study and eventually work in a host country and not speak the native language in a study/work environment.
The Professor, in her e-mail, said no problem speaking Chinese off campus.
If the Chinese students have poor EnglishLanguage skills then they won't improve them by speaking their own language at every opportunity. I support the Professor's stance. More loss to Dukes.