First of all, let me say that I think Claudia's punch has nothing to do with why Joanna feels animosity toward her. You can see at the end of the gif Joanna's wave toward Claudia which I think can clearly be interpreted as meaning something along the lines of "don't worry about it, it's no big deal." Joanna praised Claudia after the fight, and displayed no animosity that I recall in any of her post-fight interviews. Look to the source of Joanna's animosity as arising after this, in reactions to statements from Claudia that Joanna took to be disrespectful. I assume that these are statements relating to the theme of being robbed by the judges. I didn't follow their statements in social media or in interviews during which time the animosity built up, so I can't say for sure exactly how it progressed, but I think that Joanna has reiterated her claim several times that she was respectful to Claudia immediately after the fight, but that Claudia was not respectful to her in return.
That said, I think that most people view Joanna's late punch as being part of a flow that she was already into at the time the bell rang ending the fight. Maybe Claudia did not see it that way and felt she was owed a punch to make things even. Whatever was going through Claudia's mind, I don't find it credible that Claudia's punch was just a matter of the flow of the action running over the bell a little. Too much time elapsed, and it looks like she may actually be swinging around the interposed ref to deliver her punch. Nor do I find her "I didn't hear the bell" apology convincing: the ref positioned between them as he was should have been enough, whether Claudia heard the bell or not. I think Claudia was indeed genuinely sorry she threw the punch, but I think she was sorry because she knew that it could potentially be huge trouble for her and her career.