Sounds to me like...
2 people with a 3 yo (hard work)
And a new baby (hard work)
Who are most likely sleep deprived and all a little fractious.
It's not about 'obeying' vs 'disobeying' fgs, it's about presenting a united front. Op should have said" ah I didn't know you'd already said no, no daddy's already said no" and left it and discussed in private at a later point.
Op said no back story so I'm going to take her at her word. How do we know that this isn't the latest in a long line of op undermining/over ruling her husband where parenting decisions are made and this was the straw that broke it? We don't.
Being weeks after a c section doesn't make her automatically right or give her the power of veto. And if he thought she was going to be 2 mins tto get ice cream, that's very different to a slow trawl around the shops for tea post c section and a browse at the comic section.
If being sleep deprived and having a new baby excuses her of unreasonableness, then surely it does him too!
As for the only being allowed to buy herself an ice lolly if she got them all one, we don't know how it was said! "You'd better fucking get us all one, bitch" is world's away from "ooh go on then, but only if you get us all one..."
Yes, he over reacted, but we all lived with my emotionally abusive mother. My dad, my brother and I have all been guilty of "over reacting" through sheer frustration and feeling unheard.
If op regularly tramples all over her husband's input as she is mummy and knows best, I can well imagine he could feel like over reacting on occasion.
The op herself said there is no backstory. And it's highly unlikely that a genuinely abused woman would be so bold as to buy the comic or take longer than originally agreed in the shops anyway.
I am no great fan of men, but this constant assumption that man is abuser woman is always right really gets on my wick.
But no, in response to the op's question, one outburst of this nature meant he was being very unreasonable but not abuse.