No, this is not a joke. The Ministry of Health, Welfare and Sport (VWS) in The Netherlands is investigating rumors on internet forums that the keys that make a QR code valid have been leaked in France and Poland. Alternatively, it could also be that it is a rogue employee in the countries healthcare systems who creates the codes. The Dutch Ministry takes both scenarios into account and is closely monitoring them in cooperation with the countries concerned.
Hitler's code was distributed online by a hacker to show that he can create any QR code he wants. He says he sells QR codes and has shown evidence that he made some that come from France and Poland. The QR codes are also valid in the Netherlands, because they are European codes. If the secret keys, also known as private keys, were actually stolen, then all QR codes from those countries would have to be reissued.
The Dutch government claims that there is currently no evidence that the Dutch secret keys for the QR codes were stolen. For a few weeks now, people in The Netherlands a corona ticket to be admitted to restaurants, cafes, theaters and cinemas.
Of course, many do not agree with these new Orwellian laws, and are quickly inventing new tricks to circumvent these systems. Especially since many people are now becoming aware that so called "vaccinations" do not actually protect them against any virus, and that these new systems are only created as a stepping stone towards a new Chinese style social credit score system.