Let's make this clear. If you posted a selfie, it's because you thought you looked good in it. That's it. Case closed. Just own up to it. Social media is 100% about vanity and we all know it, so let's not play the shy game. I'm immediately not buying this girl saying she didn't meant to post the selfie because we can all see she looks cute in it, but there's a very clear other reason that one of her friends points out.
Accidentally posting something on your phone isn't totally impossible, but when it comes to posting a picture with a caption, it kind of is. You don't post the caption AFTER the picture, so how could you possibly comment about posting the picture on accident? It's like some weird chicken and the egg thing. What came first, the caption or the picture?