I agree with darcyfarrow that it was probably just the ultimate insult being used against Rumple to show what kind of people were in charge at that time, and to somewhat justify why Rumple would strike them all down like he did at the end of “Desperate Souls”.
The only way I think it could be of importance is if the powers that be felt bad or were pressured because of the criticism they’ve gotten about their portrayal of the foster care system and adoptive parents, and have the viewers find out that Rumple knows Bae isn’t his biological son, but not care anyway. Perhaps he already knew that it wasn’t possible he wasn’t Bae’s real father like in hjbau’s theory, but since he raised Bae from birth, he felt like he was Bae’s real father.
I’m guessing they won’t care that much though and just have it be fact that Baelfire is Rumple’s biological son.