When were these words written down -- 1994? After 1948, at least. I don't know what definition of "chanties" they are using. If the Swede "played" chanties, then obviously they are not being used as work-songs. And while some "forebitter" type songs were found used as chanties, "Sally Brown" seems to have been a "pure" chanty. The fact that someone is now "playing" it sounds like we have exited the era when chanties had a work function and we are into the era of singing them for fun.

Is there more context to this that I am not getting?

The song has no chorus -- it can't be a chanty. Unless the rationale is that he'd just give solo lines and the chorus would be assumed (??). I don't think it's a chanty. Some other kind of song, ad-libbed.

The bigger mystery *to me* is: what chanty is "Southward Ho"?