Going entirely by stereotypes, you would think that Muslims -- circumcised men who remain virgins until the 30s who hold deep taboos against drug use and blood transfusions -- would make far better blood donors than Europeans, especially with respect to a disease like Hepatitis B.
I doubt the average Muslims male are virgin before he get married, in fact even in the Middle East premarital sex are common, of course in more conservative countries like Saudi Arabia women rarely have part in it, and drug use are more common among Muslims than among Christian or atheist Europeans, simply because it's more acceptable than drinking alcohol.
As for circumcising in the Middle East it's a medical procedure often made by a non medical professional. It raise the risk of hepatitis significant.
Still this is still a sh**tty reason, the risk of an adult married Muslims man or woman to get hepatitis are no bigger than for other Europeans, if you test an adult person and find that they don't have it, the risk of them getting it later are rather low, and I fully understand why the Austrian Red Cross felt it was necessary to apoligise.
The doctor stereotyped
Muslims, not just Middle Easterners or migrants. The claim was over broad.
