Dexter actually wanted him to know how his biological son was doing, who was probably already growing up. And he was really curious, how his son could grow to be like him. And he really believed that his son would look like him. Although it may not be 100%, but maybe all of that will materialize above 80%, the presentation of their resemblance, because it is indeed a werewolf, has definitely inherited a strong gene for its offspring.
And that gene he must have passed on to the child that was once conceived by Stella. Even though he couldn't know for sure the truth, he never gave up on knowing everything. Is it true or not, and in accordance with the assumption.
