Hiya. That's indeed by design. The Warhammer games are pretty huge and there's three of them, so there's a lot to be written. As a result it has its own dedicated sister wiki that you can find here.
The split was before my time, but I'm fairly certain it stems from quantity of Warhammer content, evident by their 10,000+ pages (double of ours). We only have a handful of very surface-level Warhammer pages that mostly just act as redirects to the other Wiki, so it would make sense for them to be something of rarity when you're cycling through random pages.