Nah, I don’t think that’s really self deprecation or calling her a slut- saying she’s ‘used to the attention of boys’ sounds like it’s just saying she’s familiar with guys trying to get close to her, but it still over-estimates how close other guys really get when you put the statement next to what just happened.
Regardless, he didn’t see her react all that strongly to the incident, so that reinforces his perception that it was ‘no big deal’. She only let herself express her shock after she noticed he wasn’t looking.