This mechanic used to work when 1.17 came out and before. It makes no sense that I can place the zombie in a minecart in the exact same spot and it can convert a villager into a zombie villager. This is how most villager conversion chambers used to work.
Can confirm this is happening on 1.21.21. Playing on a realm. Minecart stops on a powered rail. It seems to be within the chunk so it doesn't look like chunk borders/corners.