no idea how they would came to such knowledge ;)
would guess more you possible missunderstood some.
how i said tyrolean can never be "a blend of local dialects mainly German and Italian" as is a dialect of german and has nothing to do with italian language.
just at Trentino-Alto Adige meet two language areas - the german and italian. the province Trento/ Trient always was most italian-lingual and province Bolzano north of it most german-lingual. so also many people bilingual which speak both languages. and in documents, records you never will find a dialect of any language.
no attachment to see if italian or latin?
would guess more for latin that time....maybe.