Half that would pay for the sort of lifestyle he talks about in his original post
Not with a free standing house that fits that lifestyle. And certainly not with any savings. A western expat professional with a family of four would be scraping bottom if they were not able to put away at least 4000 PLN a month, and that's really minimal.
Very few jobs in Bialystok pay that.
I'm assuming from the wording of his question that he is being sent by his Dutch employer and will be earning Dutch wages while in Poland, and that he is at least middle management.
I think the problem comes from foreigners who go to Poland expecting to live the life they were living back home
It's not exactly a problem if they are earning expat wages and have money to burn. A bigger problem is foreigners coming here expecting to live as cheaply as Poles, and Poles like you telling them that they can. You kind of perpetuated that with your video quotes. What may be a comfortable wage for an average native Pole is horribly low for a highly qualified foreigner, or for a highly qualified Pole, for that matter.
Foreigners generally don't speak any Polish, and don't have a local network of family and friends. Both of those raise the cost of living a great deal. On top of that, they often have children that need to be sent to expensive private schools, which can cost as much as 4000 PLN a month per child. Poles are generally honest when dealing with foreigners, so the "gringo tax" is not nearly as bad as in, say, Central America, where price gouging is the rule, not the exception.
That is why statements like "you will be earning twice the local median wage" are completely meaningless to a expat. They don't give a rat's a$$ how much the locals earn. Their own wages per se don't matter to them, nor does cost of living per se, except as to how they impact the only financial figure that does matter to them, which is how much they can put aside at the end of the month in their savings or retirement account or in their kids college fund after paying for (what is for them) a comfortable lifestyle. Without savings, the job is not worth taking, unless it somehow has a very, very high probability of guaranteeing advancement and higher savings potential in the future.
For westerners, this is rarely the case. A decrease in savings potential is an opportunity cost that few are willing to incur, which is why so few westerners come to work in Poland compared to how many Poles go to work in the west. Indian engineers, on the other hand, may be willing to slog through a year or two of working for substandard wages in Poland on the assumption that this will enable them to get a much better paying job with much higher savings potential in the west in the future.