I get that, you're just trying to understand it. Some comments can come across over the top and you may be like wtf that's nuts but some have experienced things that may relate to this sudden personality switch.
Again, I don't know you or him and have little to work from so I can't say for sure but I suffer with dissociation which has come from being in an abusive marriage for over a decade.
The problem is if you don't know about it or understand the signs, it's very easy to fall into it. I was similar to you and felt it was okay because we were fine, we weren't arguing was relatively normal and happy apart from a few minor blips here and there. Those blips weren't massive arguments, nothing obviously wrong just a bit off at times. At those times I excused it, brushed it off and tried to understand and thought must be struggling in some way, had childhood issues which they did too.
I was wrong and it became something else entirely and now looking back all the signs were there from the beginning and I didn't listen to my gut. I have been living a lie basically the person I met and married is not who they are today and in the end they fully switched on me right in front of my eyes into someone else. They showed me who they really were all this time and it was evil, totally void inside, glossy eyed and hate filled.
So yeah, dissociation happens but what others are saying is true in my case also. Strong and offensive views that most people would not say out loud, no empathy, no remorse or guilt, a vacant stare and silent treatment when challenged.
The only thing that strikes odd to me is if he was perfectly fine afterwards, in my case that's not how it is. I come back but I am disorientated for a fair while afterwards and need to recoup. Normal to vacant to normal and carrying on fine, no.
At the end of the day it's your call but honestly if this starts happening more frequently over different things and it is more like an instant switch on and off be wary. As others have said if you feel anxious or have feelings in your gut, trust them.
Again, not fear mongering just advice take it how you want but wish someone had said same to me back along, wouldn't wish it on anyone.