I literally worked in a research lab working on islet cell therapies for diabetes in the US. This has actually been done many times before with cells from cadavers. It has been successful, although most the of the time the person reverts back after a few years
The issues we were trying to solve in the lab were
Finding a good place to transplant where the cells will last: Implanting in the hepatic region (liver), which is the most common place to implant, is toxic to the cells over time hence only lasting 3-5 years. The cells need a really good blood supply and the volume you're transplanting can't be easily transplanted in the pancreas or kidney capsules (where many successful studies were performed in mice and rats)
Being able to consistently make a high volume of stem cells that are fully grown into insulin producing cells:
Cadaver cells usually require 3-5 donors for 1 person and require the receiver to be on lifelong immunosuppresors due to the immune response. Depending on the kind of stem cells, the patient may still even need immunosuppresors due to the cell type you're converting from
All this the say - the article says nothing about where the cells where transplanted, where they came from, or whether the person has Type 1 or Type 2 diabetes. Although it is still a feat, it is likely not the first time it has been done, and we're still a long ways off from a cure