The guy is from the U.S evidently, when living abroad and an U.S citizen you pay U.S taxes and taxes abroad which is a hassle, however you can take off your taxes from one or the other from your income (can't remember if it is take off from U.S the other taxes, or take U.S taxes off the other) maybe you can do either one and so you choose which is more beneficial. It would obviously be more beneficial to deduct U.S tax from income before paying EU tax.

All that said I'm not sure about this guy's tax rate, just there are probably wrinkles here that will make things come out weird if not taken into account.

on edit: although his phrasing makes it sound like it is applying to all Danes, which anyway would be weird, why would you care what Danes pay if your concern is figuring out the cost/benefits of you (or someone like you) moving somewhere.