As others have already pointed out, a lot of what you're hearing as "out of tune" is simply a deliberate (or perhaps intuitive) specific way of pitching. What it has most in common with is the fiddle styles of Scandinavia, which also uses those quarter-tone pitches. So in a sense, it's not surprising and all very joined-up: from Scandinavia to Scotland and Ireland, and from there to the US. Listen to African spike fiddle playing and singing; listen to some Scandinavian fiddle. The return to your old-time stuff. You'll see what I mean.