Allow me to explain why to me Anton and the lost brother are two different people and why to me is weird when I see someone automatically assume Anton was taken by fairies.
First, before D mentioned Anton's name, he explicitly asked Kitten to not say the brother's name. I've seen people argue that D was so emotional he accidentally said it, but seeing it from a writing perspective, it doesn't make sense for a character to not want to hear something and say willingly the exact thing later.
And second, in Anton's playlists (1, 2) there's music from the 90s and early 2000s. If he was taken in 1988 why would he have music from those times? I find it hard to believe the fairies let him out given how he got turned into a slave.
Now this is just my interpretation and I'd love to read other's opinions on the matter, after all I also thought at first Anton was the lost brother, and it was on my second watching of Ghoul Lore that I came up with this. Plus I'm deeply fascinated by him despite the little official info we have about him. I'm still very ignorant on Changeling lore and how the Fae work in general, so I could be missing smt.