There is very little experience of traditional Kava drinking in Europe, but the three Polish kava shops opened one after another, so something must be happening in the right direction. I doubt that it's all consumed by local demand. Cost base in Poland is very low (which is why it is attractive to do this business in Poland) and yet they are selling kava at prices you see in the Western markets plus international bulk shipping costs. So, my guess is they do significant business in other EU countries.
I doubt there are an issues with sending retail kava parcels to other EU countries due to single market and no customs checks. All questions raised here about the details how this is happening despite different regulations within each country are valid, but I think there are very few people who know the answers, it just happens (until it doesn't, like in the UK after the blanket ban on legal highs in 2016; when they realised coffee and scotch were banned, they specifically excluded those).
Why Poland? If I remember correctly until recently kava was banned in Poland as a hard drug with jail time. This has changed. Don't know the details, but there were claims from Polish enthusiasts they were actively campaigning for it. It could have been the case that the nationalist/populist ruling party, which has been in power for a good number of years, wanted to show that they are efficient and can make a change. If that's the case, then even though the process is not over yet, as pointed out above, chances are that kava will stay legal or almost legal in Poland. Otherwise it would be a U-turn on a new policy/regulation from business perspective.
Regard the peculiar demand for a specific cultivar, I would be very surprised if that was based on local demand. Many probably do not even know there are different cultivars and think these are just exotic names. It's probably just this specific supply chain the owners have access to somehow.