As I have noted several times on FR data on Muslim populations in Europe appear to be almost totally unreliable.
Well people tend to exaggerate, and sometimes lie to convince you. For an example, not everyone from Africa are Muslim, but when an author wants to exaggerate, they count all African immigrants as Muslims.
E. Vesselbo, a sociologist in Denmark projected that by 2060, 50% of Denmark's population will be Muslim. His projection assumes accelerated rate of immigration, plus 2nd & 3rd generation Muslims maintaining 1st generation's birth rate.
How realistic is that? If anyone thinks the 2nd and 3rd generation are going to have 4 children/family, they're delusional.
BUT it doesn't take a majority to have major impact on a nation's politics and foreign policy. Look at our Jewish and Cuban lobby.