On average, yes. But if you look on a voting map[0], you'll notice that the majority of those votes comes out of the former DDR. In many other areas, much less than 1 in 5 voted for the brownshirts.
If you look even deeper, at people's actual attitudes[1], you'll see that far-right positions are approx. equally distributed in Eastern and Western Germany - the kind of people voting AfD in Eastern Germany (currently) just vote CDU in Western Germany.
No, the point I am making is that it very much depends on their location if this "1 in 5"-average is even remotely true. And looking at overall population statistics and concentration of jobs, it's comparatively likely that somebody migrating to germany is _not_ in those areas.
>> This is comforting, as an Argentinian living in Germany. 1 out of 5 people here voted for the AFD...
My fundamental aim here was to show the poster, that it's likely not as bad where they are - and since they are a migrant, I assumed that they were likely not in those really bad areas. Intended as a positive message. Sadly, I apparently butchered the delivery of this message, as several people interpreted it completely differently.
[1] = Leipziger Autoritarismus-Studie, https://www.boell.de/de/leipziger-autoritarismus-studie