Well the Study Visa/Student Visitor Visa was a route we tried 5 years ago and it was refused.
We did not find the process anywhere near as easy as your Chinese friend and (please take this in the spirit it's intended) there are a number of serious omissions in the story as it has been told to you:
1. You need to PROVE you have a shitload of money which will sustain your living expenses throughout the duration of your Course. At the time we tried it was a minimum of £800 per month - so for a one year course you'd need to have (and demonstrate you had) "recourse to funds" of £9600 in an established bank account in your name for at least the last 6 months
2. The only way around that (if you're unable or unprepared to deposit 10,000 knicker in your BFs bank account for 6 months) is to claim that YOU will underwrite that sum of money and then the onus falls on YOU not only to PROVE you have "recourse to funds" but (and here's the bitch) PROVE you will give those funds to him. Quite how you are supposed to PROVE what you will do in the future remains a mystery and that was the excuse they used to refuse the Visa - that they "were not satisfied" that although I had deposited said funds in a dedicated UK Bank Account and had certification to prove it, that I would actually make those funds available to him if and when he arrived.
3. As the "sponsor" you then have to submit yourself to intense scrutiny - this involves providing the title deeds to your property, your bank statements, your birth certificate, even the logbook of your car!! All of which must of course be notarised by a solicitor at your own (considerable) expense.
So, to sum up, yes it could be something to look at again but it's something we tried years ago and either your Chinese friend is extremely well off on his own account or there are aspects to his application he's not telling you.
The other aspect I find confusing is that he seems to have gained a Study Visa whilst in the UK on a Visitor Visa - we were told yesterday that this simply isn't possible and that any application for any other Visa must be made from your country of residence - which would involve going back to Vietnam and starting again.
But I do appreciate you taking the time to post a suggestion