I think you misread the latter part of the sentence - OP said they provided the raw text in a comment. This is no different than some other paywalled articles posted here where the first comment usually just links to the web archive for a non-paywalled version.
Is it really unfair? Your link isn't accessible to a non-insignificant portion of the HN audience, therefore it seems reasonable to flag it.
It isn't reasonable to expect/force people to read comments before flagging content for being inaccessible.