Does Cabal Paladin's ability trigger when playing an artifact land?
No, it doesn't trigger. Lands are played but not 'cast'. There is a ruling below the card in Gatherer which explicitly states so:


  Lands are never cast, so abilities that trigger “whenever you cast a historic spell” won’t trigger if you play a legendary land. They also won’t trigger if a card on the battlefield transforms into a legendary land, as the Ixalan and Rivals of Ixalan double-faced cards do.