He is 100% Austrian but from areas which used to be ethnically Slovene in the Middle Ages (and later).
Didn't you read his posts? All of his ancestors are from Carinthia and Styria (or Medieval Carantania):
https://en.wikipedia.org/wiki/Carantania
He is descended from Germanized Slavs.
No, he just doesn't know his Slovene ancestry. Apparently they were Germanized long ago.
By the way what is "100% Austrian"? Austrians are a mixed group and have a lot of Slavic ancestry too.
Austrians got their language from Bavarians, but they are not 100% Bavarian-descended.
If you used East Tyrol then you did not omit Slavic imput, there are many Slavic toponyms in East Tyrol.
Austrians without Slavic input = Bavarians (except for North-Eastern Bavarians who have some Slavic).

