Nope. MC says they "got along as well as two people could" who were in competition for a limited resource; that's not the same as "good friends" since there's no indication they enjoyed one another's company or spent time together socially, merely that they were civil to one another. It's also worth remembering that he acknowledges barely remembering Stephi from that time period, and he wasn't friends with her anymore, and he had no idea of the particulars of her relationships or thought processes, and a lot of what he "knows" was very possibly just rumour; remember, he also thought Alyvia was a slut at this point because of rumours, and he was wrong. He's a wildly unreliable narrator; he's been wrong about the behaviour (and the reasons for that behaviour) of almost every other character so far.
And do you think that broader use is the one that
w123t4 was intending, or do you think from context clues that when they said "act as a bitch" they meant to behave in an aggressive, belligerent, or spiteful manner?