Of course its sincere, but that's it. I write paragraphs of text to someone explaining exactly what's going on and they just say "I'm sorry". Please tell me I not the only one who thinks that's rude.
If they don't know how to handle the situation, they're better off not saying anything because it just makes me feel worse.
True, usually it's just for attention.
They feel like their real lives are so boring that they feel the need to do stuff like that. And then they can start to believe it's true, like if someone is lying about how they have Bipolar Disorder, they start to feel, ever so slightly, like someone who actually has the condition. They expect to be treated like they have it IRL too, even though it's a complete lie.
I know because I was like that when I was a preteen. I didn't create an entire story separate from my real life, but I tended to exaggerate things, especially when describing how I looked. But I learned from that and moved on.