Back when the monk first was introduced, I mistook him for Thorfinn (because of the shaggy hair) when his beard wasn't visible & I still think he looks like an older Thorfinn, but I was certain that there was nothing to it.
Even if the monk knows Thors, it might just be a fateful encounter they've had in a church or something with them discussing their philosophies or influencing each other with that idea of what a true warrior should be like & the quest for love.
It'd be interesting to see how a conversation between the monk and Thorfinn would go. Especially if Thors' ideals are brought up, Thorfinn must've spent the last ten years pondering about his father's words.