I don't think that far-left was primarily only written because of the tax returns. I followed some links in the article and came to this twitter thread which might explain where that notion comes from: https://x.com/lukerosiak/status/1885523747425399247
(Disclaimer: I don't live in the US and don't want to take any political stance with this)
(Disclaimer: I don't live in the US and don't want to take any political stance with this)