Plague naturally exists in many parts of the world, New Mexico for instance has one or two cases each year, mainly only reported locally. Where I live for instance is one such area. Sudden Die backs of ground squirrels or gophers, rodents and it is probably a wave of plague going through. Mountian lions will eat these dead animals and die of plague as well.
Why five and just in one area..most probably these people have fleas and no immediate access to health care services.
They live with fleas so such can spread easily from fleas to humans. Most probably humans with close contacts with animals that harbor fleas and occasionally bite humans. Perhaps a agricultural area where people live closely with animals or where such is traded.
That in the main is why plague is no longer the great killer it once was. Early treatment prevents progression into the pnumonic phase and fleas on humans or exposed to humans have been greatly reduced.
The pnumonic form is transmittable from human to human but often this presents only in the later stage of the disease and many never develope this stage. So many pneumonic would suggest others with plague not yet diagnosed. Nonpneumonic and it is not largly transmitable human to human, except perhaps if one engages the body secreations themselves such as in body disposal.
In the us cats to human is most common with the fleas or with the human exposure to the bodily secreations of the sick cats.
Dogs don't tend to be symptomatic with plague it seems. So fleas to dog to human would still be possible but not exposure to bodily secreations. Some dogs become symptomatic but many do not. Cats it seems always do.
So if you go to that part of Tibet don't cuddle the cats. Use deet.
Plague in asia had somewhat a similiar history to plague in europe. Keep in mind probably roughly half of humans in europe died due to this at one time. In asia it was more on a city to city behavior. Some cities got it some did not. Ports cities and such were most exposed. Perhaps consequenct to trade from other global areas.
REading the article I would disagree with content a bit. The symptoms abscribed to plague actually fit flu not plague. Swelling of lymph nodes(which are present throughout the body) pain in such areas would be a early indicator to my opinion. As mentioned many never develope to the pneumonic phase. If you develope to the pneumonic phase I'd suggest you are critical and late untreated stage. I'd bet my bottom dollar it was one case of pneumonic and four others with plague but not pneumonic, as only one is considered critical. Or all are critical and they are not reporting that correctly.
So many pneumonic cases would suggest to my opinion other untreated or unrecognized cases in the human community there.
"This order considers that progress can be achieved more rapidly during a single month of self-transformation through terrifying conditions in rough terrain and in "the abode of harmful forces" than through meditating for a period of three years in towns and monasteries"....Takpo Tashi Namgyal.