I always think that if you have to rely on technicalities to make yourself feel better, you've probably done something not very nice.
Sure, TECHNICALLY Oliver and Carrie aren't together anymore, and technically he doesn't owe her any loyalty. But coordinating romantic Insta posts in Paris to confirm you're at least seeing someone - a person who you've known for a few years and worked closely with during your relationship - only three months after the end of a years-long relationship? Bad form, imo.
That's not to say I think Carrie has handled it particularly well either, she should absolutely have taken the high road and never mentioned him again beyond explaining that she was no longer in a relationship. TECHNICALLY it's not wrong of her to share her side of the story, but it still feels wrong when the other person is maintaining a (somewhat) dignified silence (that's probably mandated by their work contract, let's face it).
Technically they've both done nothing wrong, but in reality they're disrespecting each other enormously and it's not a good look.