@Forikorder maybe? but what he is doing is actually good right now because he needs to let her mother know about them as soon as possible. ITS ALL ABOUT THE FIRST IMPRESSION. So, rather than hiding to her mother about their relationship. Cuz, that will make the relationship of both mother and daughter go bad because of the secret that they hide from the mother. Its called "Trust".
And at the least he will have a slight chance of changing the mother decision and she might accept their relationship in the future.
Cuz, right now as I will said it again its about first impression and making yourself known. "get to know each other phase"
Its risky but its worth it.
what I am trying to say is that it would be good that he will be accepted and became part of her family
for example, Horimiya where Miyamura is always at hori-san home and he is arlready accepted by hori-san mother and father
if i am correct the mother is some kind of the head of the family and is a stubborn and persistence person that will try to break their relationship? maybe? just guessing though. XD