It seems that Aidan Gillen guessed that Arya would be the one to end Littlefinger years ago.
Arya was over in Essos, learning how to kill from the Faceless Men at the House of Black and White.
It was difficult to imagine how they would end up in the same place for Arya to kill him, but Gillen made his guess all the same.
Who could have thought back in 2015 that Littlefinger would be executed in Winterfell by Arya, on the orders of Sansa and with the help of Bran as the Three-Eyed Raven?