I've seen this pattern before too. (I was the child in a similar situation). It goes like this:
(1) DH acts like an arse to punish you and to show you that this is what happens when you don't act in the way he wants you to. He offers or threatens to leave because, in his eyes, that would be the ultimate punishment for you. He's going to deprive you of his very presence. That'll teach you!
(2) He sets up situations to show you that the reason he isn't looking after you is because he chooses not to, rather than because he is unable to. This would've been why he came home that day to use the toilet and then immediately left. See! I could've come back to make you a quick drink but I choose not to! That'll teach you!
My mother's DP used similar tactics. For example, on a day that he was meant to be helping to move furniture for her after work, he booked the whole day off at the last minute and spent the day and evening sitting on his backside instead. See! I could've helped you but I chose not to!
(3) When that particular tactic fails, it's on to being Mr Nice. Look at me! Aren't I wonderful? It's obviously not me that's the problem in this house. See how much you need me? The added bonus for them is that the DC see their mother being appreciative of the help and then their own fear will start to seep back in. He's wormed his way back in again. This time he's going to stay.
(4) If being Mr Nice has the desired effect, give it a few days or weeks and Mr Nasty will return and you'll be back where you were in your OP.
They always think they're being clever but don't seem to realise that they're just following the same tired script that every other abusive man like this does.