@Thembs I feel like you're coming at it from the wrong mindset. The Grandpa clearly believes that his grandson is straight (probably because this is the default mindset and he currently has no reason to feel otherwise). As a Grandpa who has only one relative and is often alone - he is hoping to make sure that his Grandson is not lonely like himself (he wants him to be happy and supported with a family). Obviously the best way to not be lonely, in his eyes, is to get married and have children so that you have strong family bonds. He's attempting to help him along this path. Note that its not like an arranged marriage or something - he's not force the dude into anything that is permanent.
Now, if the Grandpa comes to realize that his grandson is gay and then disowns, hurts, berates him, then your comment becomes a bit more fitting - but for now, he's just a concerned older man who does not understand why his grandson would choose to be alone.