Well, again, the text of the video. No more but no less either.
It's not merely showing that already known basic chemistry works as we already knew it worked.
It's almost like but again not merely showing that you can make your own cottage cheese at home instead of buying it as a commercially made product.
Countless medecines, and their delivery mechanisms, exist that could be produced in a more diy way, but most people don't know it, because of basically PR driven by the people who make money from medications and health care in general. That PR encompassing both ordinary direct messaging to the population and doctors, and lobbying for regulation and direct influence over regulating bodies and standards bodies by being members themselves, etc. The true issues of quality control and safety etc have been grossly over-used to justify removing options and control from end users.
I did not know that you could make your own epi pen. That is the kind of thing that everyone should know. I don't mean that everyone should know how to do it, I mean everyone should know it's possible and always there as an option the same way everyone knows you could make your own cheese.
That is one example that answers both questions. It proved the concept that such a thing is possible, and I myself also happened not to know it before watching the video.
I don't think it is invalid or not a proof of concept even if there already exists people with the right knowledge such that they consider the contents of an epi pen "basic chemistry".
It is still a revelating proof of concept that one can produce one's own epi-pen, and that the only thing preventing countless people from being able to take advantage of such a huge practicality, is a combination of various forms of artificial barriers that should all be insubstantial, but in the end they do end up acheiving the result that the epi-pen producer wants. No one makes their own epi-pens nor produces them in a cheap generic form (in the US).
That particular example isn't even new. When I google "make your own epi-pen" I see it comes from 2016. That does not mean it's not a proof of concept, it just demonstrates how those insubstantial barriers never the less worked. Not just because I personally did not know about this public thing that was there to be googled since 2016, but because in fact all the people who pay US health care rate for epi-pens unwillingly.
I think it doesn't matter if a concept is new or already known to some. A video demonstrating that it's possible to start a fire without a match is still a proof of concept even if some humans have known how to do that for thousands of years.