Not that Celebrity aren't doing the gouge in other ways, but that article is just sensationalism, not a genuine trend against solos.
I've only seen it arise in very rare situations before, and checking it I believe to be the same issue. The pricing difference doesn't even exist now so it may only have been for a short while while different prices were updated, or maybe they corrected it after that was posted.
Notably the poster didn't include the sail date so had to do some digging and it turns out it is only 2 weeks away - 28 Jan 2024. When it is down to the last minute most cruise lines have last minute specials and sometimes they just target the most common twin share as a promotion, (and sometimes other niches e.g. seniors, locals, certain TAs.). So in this case they look to have done a price reduction on the lead in twin share rate, while leaving other rates untouched at the time that poster checked. As said, the pricing is now equivalent between solo and twin.
Also while it was only a specific case that publisher didn't note that but implied it was general and most/all pricing, saying "Celebrity Cruises has really gone overboard (pun intended) with its new pricing policy that discriminates against solo travelers.". If they were genuine they would have checked other sailings to make that general statement, which makes me think that the lack of dates was deliberate and just a sensational article for clicks. They say they are an experienced cruiser, so would be familiar with how prices rise and fall at different times, and mention they know different discounted booking methods, which this falls under.