All those so quick to defend a man who not only hit his child hard enough to bruise, and couldn’t give a fuck, in fact his sole response was “he needs to learn” I hope that you don’t apply that bullshit in your own lives.
Sure, one explanation is that the husband doesn't care, honestly.
Another possible explanation is that his brain was in shutdown spiral mode thinking "Oh shit oh shit oh shit, what the fuck have I done, my wife is going to go spare, oh my god I've never hit my son before, what if he hates me forever, what if she leaves me, what if she never trusts me with my son ever again, shit fuck wank bollocks tits, I'm a goddamn idiot" and he just came out with "Well he needs to learn" because he's unable to vocalise any of that without sounding demented, or because he's a man and many of us have had bad socialization that prohibits admitting mistakes or talking about feelings, especially both at the same time.
I'm not excusing child abuse, but without being telepathic, you have no idea which of the two scenarios described above is closer to reality. Assuming the former possibility without considering the latter and recommending social services get involved in an otherwise healthy and completely functional family is lunacy.