Let’s start that from the fact that everywhere around Kazordoon you can see Knights Vocation presence as an example:
Dwarven Statue (with Axe) -https://tibia.fandom.com/wiki/Dwarven_Statue_(Axe)
Dwarven Statue ( with Hammer)- https://tibia.fandom.com/wiki/Dwarven_Statue_(Hammer)
Dwarven Statue ( with Mace) - https://tibia.fandom.com/wiki/Dwarven_Statue_(Mace)
Even the quests related to Kazoordon will have a connection with Knights- the rewards are mostly for Knights use only (Crusade Helmet Quest, Iron Hammer Quest, Circle Room Quest ). Of course – it is not strictly knight-only thing, but the majority is about knight weapons or their creation.
Since “Dwarfs are a very ancient human-like race. Once they were famous all over Tibia for their craftsmanship” and they were using typical sword weaponry/ equipment they would master they craftsmanship in these areas. Therefore, their symbol of culture would be weapons such as Axe, Hamer, Mace- which they are proud of.
Considering that Rehal is a Royalty of Dwarfs it is more than right that he will be linked and associate to Knights Vocation. Consequently, the Royalties would be able to do more than “normal” citizens, for example, teach spells for knights (for those who deserves to know!). It’s like Emperor Kruzak & Rehal are selling promotion, Kawill (Geomancer Chief) or Pydar ( Head of Pyromancers) are selling the blessings. Another person who is selling similar spells- Duria- is a Knight Guild Leader of Kazoordon. Notice there are no other Guild Leader representatives apart of Etzel (with the title of Sorcerer Guild Leader connections to Sorcerers are also visible in Kazoordon & not only there- see Sorcerer Statue (Dwarf) ). The fact that Rehal is allocated far away is a part of the quest (Rehal has been imprisoned by Trolls). It is out of respect to his status and history that he can teach Knight spells, despite being in the Prison cell.
It is an amazing addition to the history History of Dwarfs & Kazordoon giving it more personality and deepness.