Well, if one's on the extremely far right-end of the political spectrum, everything and everyone else looks left. Besides, if one just excludes economic politics (in which the AfD is hilariously out-capitalist-ing the FDP) like the far-right populists generally do, backed by wealthy people as they all seem to be, the mainstream opinion of simply accepting other forms of family or concepts of living together outside of what politicians in Germany call the "core" (father, mother, children) family is something that can be seen as left insofar as the left leaning parties are the ones pushing for more sociall progressive policies.
It's not like the CDU (or our equivalent, the ÖVP) were at the forefront of opening marriage for homosexual poeple. They hemmed and hawed until they were just forced to. Angela Merkel was chancellor at a time where society as a whole moved towards more understaning and acceptance of alternative ways of life. One act of accepting refugees might have caused a cascade reaction landing us in some dangerous waters in this day and age, but left-wing does that not one make. Certainly not the CDU, and even less their Bavarian appendix.