jack dawson was being metaphorical he isn't royalty of any description he's a peasant he isn't even a king of peasants if i had a dog and my dog had a child and my dog's child had a pet that would be jack dawson lord voldemort however is a dark lord which is to say a warlord with magical powers warlords actually rule people thereby qualifying them for the title of lord furthermore no i don't know you in real life you just remind me of someone i used to know