Plenty of fanwriters also write profic. That doesn't make their fanfic any less "fan". It's the same with illustrators. I think the only grey area is when people who work officially on a property also post non-official art for the same source. There are a number of female fanartists who work as illustrators too. And you see the same type of art posted by female fans as well. Things like poster mockups, covers, fake picture books in old styles...
Like gnatkip's HP picture book pages "Wonders of the Muggle World":
Actually a lot of gnatkip's art is style homage as well as fanart, and that is common.
Like HP Fringeart regularly runs imitation challenges where HP fanart is done as style homage to other art and illustration styles.
Same for the fake paperback covers, female fans do those as well, like Hope for Torchwood:
SPN as 60's movie poster:
more SPN movie posters:
And of course there are countless of macros and the like. That fanart linked in the article is pretty much like any other gen fanart that is a bit style-oriented instead of solely character-focused, IMO.