I've looked into his more recent past and he has said he's a regular Dem, not a progressive.
Also worth noting, the term progressive has itself been somewhat hijacked by the activist left since the above tweet came out. Its now come to mean a tidy suite of policies exemplified by the likes of AOC and the squad. This was less so the case for most of the 2010s when ordinary Dems would call themselves progressives, but still adhere to what is today mainstream, corporate Dem orthodoxy. Hilary Clinton for example, insisted she was a progressive when running against Bernie Sanders in 2016. Fetterman would seem to be in the same category given that no one has every mistaken him for an AOC type in the present.