This is an interesting article. From what I can tell, Kufri is about 8200 ft. in altitude. Yaks in the United States tend to do well at much lower altitudes but there seems to be a temperature component as well. I have never heard of one dying from too low an altitude. Domestic yaks are all the result of some cross with domestic cattle (bos taurus or bos indicus). One of the reasons for this out crossing was to help them deal with lower altitudes. I would have to assume that these yaks were the domesticated variety, as the wild ones are not typically something you would ride. Seems like a bit of ideological coloration is involved with the issue and its reporting. Read the article and let me know what you think?

http://timesofindia.indiatimes.com/city/chandigarh/Lowly-owners-exploit-rare-yaks/articleshow/5137460.cms