There’s a lot of ambiguity in the article when it comes to S33.
The article’s title indicates 2.7.8, not Season 33. And in the article, it’s worded rather informally as “The Shades of Nephalem seasonal theme will also be available to play during the PTR”. Instead of ‘The season 33 theme will also be available to play…’.
Additionally, the link to the Shades theme goes back to season 22’s article, instead of a new season 33 article. As if to only provide info on the theme, not to officially announce it as S33’s theme.
Even more, the cosmetics don’t align with the old season rotation that, so far, has been in unbroken chronological order since the rotation started.
All taken into account, I wonder if the PTR is not meant to be representative of season 33 itself. But instead, just something thrown together to test the Mac exes. Bliz may have just used last season’s basecode but changed theme from Archives to Shades.