I think he means that Littlefinger is the actual lord of Harrenhal without ever setting foot in it, like Slynt was. Slynt is not recorded as being lord, though.
Because it's not the same. Littlefinger was made Lord of Harrenhall after the war ended and no one disputes his claim, the castle is held for him. Janos Slynt was made "Lord of Harrenhall" at a time when the war was still ongion and the castle was actually held by the enemy. Just like how Garlan Tyrell was made "Lord of Brightwater Keep" even those the Florents still hold it and he has never set foot inside it.
In game mechanics terms, niether of them are ever actually the Lords of those castles, but they are givena strong claim to it, which allows them to try and enforce their "title".
I'm also happy to note that I was right about southerners being able to become skinchangers![]()
No one ever said they couldn't and there is nothing ingame stopping them. You just have to be a southerner who follows the Old Gods religion.