The FDP is not libertarian by any measure. Much like the CDU they claim the social market economy of Germany as one of their achievements, which would be called outright socialist in some American circles. From an American perspective they can be compared with the Democrats in the US. Of course the whole political spectrum of America is further right than that of Germany.
I would hardly call the FDP libertarian.
So neither liberals nor libertarian. What are they then?
Conservatives for the rich with a modicum of backbone to appeal to people who wouldn't vote for corruption scandal parties like CDU but Christian Linder seems to be losing his backbone as well.