Yes in Antonella's presentation she shows some drawings that indicate that the epithelial cells were derived from human (iPS) cells too, but other than that, all the other materials we have from them up to 2019 indicate they were using mice cells. But that is not really a problem IMO because since 2014 it's already known how to deriver folliculogenic epithelial stem cells from human IPS cells:
https://www.nature.com/articles/ncomms4071
I guess that's why Antonella said, regarding epithelial cells, that they were "optimizing existing protocols". The thing is the novelty on their part was the discovery of deriving DP cells from iPSC so that's the part they were focusing more in the early years of their research and even nowadays give it more importance. But as of now there is no reason to believe they can't derive both kind of cells from iPSC, fundamentally the problem is solved, it's currently only a matter of optimization and "engineering" to get it perfect, according to them. Also, I don't know if you are implanting the hair gems in mice you must use mice epithelial cells? It's a possibility.
Regarding the phrase "Unfortunately human DP cells are not suitable for this purpose because they cannot be obtained in necessary amounts and rapidly loose their ability to induce hair follicle formation when cultured." -- you are right, they solved it. How they solved is by not trying to expand DP cells directly. They first expand iSPC (which is supposed to be very easy), THEN they derive DP cells from it. Same end result (you get more DP cells) but different method. Supposedly if you try to expand the DP cells themselves they will lose their properties and it won't work. This is the part where the Stemson researchers got their scientific breakthrough as nobody else had done it before. They even secured a patent related to that process.
