Depending on your experience with the body positivity movement that phrase can bring up several different images in your head. Maybe of hashtags like woke up like this, or no makeup, or simply love myself. Maybe you think of women running free naked in the woods. Maybe you think of white women with flawless appearances and feel worse about yourself. Whatever image that comes to mind, we have to admit that the body positivity movement is often misconstrued in several ways, especially with younger girls.
Now, loving yourself doesn't always mean liking yourself. What do I mean by that? I mean exactly what I said. Loving yourself doesn't mean not acknowledging and accepting your flaws, physical or otherwise, it's learning to live in and be comfortable with yourself, in your mind, in your skin because it is the only one you will get. Plastic surgery can only change so much.
For example, I have never been a fan of my nose. I got my dad's nose, much larger and less "feminine" to use a dangerous word. We have a tiny bit of Native American ancestry on my Dad's side of the family, and that is the only place you can see it in, the nose. Now, my mother has a much more petite nose, and when I was younger, I was upset that I hadn't gotten her nose. There are issues with that because I wasn't accepting my shape, but not as someone who is much more comfortable with their body, I still will say I don't like my nose that much. I think smaller noses are cuter, probably because of social conventions of femininity, but also I just like them more for aesthetic purposes.
I am not crying in my room over my nose and desperately saving up money to get a nose job, but I am not lying to myself that I love every single thing about my body. You are always going to like some things more than others. So while I hate my nose, I certainly love my freckles.
This type of thinking also extends to the level of personality and mental state. Being mentally healthy means accepting your flaws and working to be the best human you can be every day. This is in opposition to people who are willfully oblivious or ignorant of their negative personalities traits and blame others around them for any problems. Most problems between two or more persons are never entirely one person's fault, though someone may be more at blame in certain situations. Recognizing and acknowledging how you have been contributing to an issue is important and vital to problem-solving.
Really at the end of the day, I am still annoyed at something that was happening in high school because I apparently just can't let it go and move on (see acknowledging your personal failures above). A lot of girls in my high school, and to be fair they were young and dumb, often would say the phrase, "well, they were just jealous." I guess that may be true in rare cases, but that line of thinking is very problematic. Not only does it refuse to acknowledge personal failures, but it is judging your self-worth based on someone else's attitude. You shouldn't care if someone was jealous or not, you should be focused on yourself and your health and not care what someone else is saying about it because you are the only person who really has to live with yourself.