It could still count as bullying. Teasing can be fairly mild but it can also be taken to considerable levels of cruelty. Some kids are just mean and you can’t always be sure how far they will go with their torments.
It’s also possible that she might be withholding details of more serious types of intimidation to prevent outsiders picking up on other ways to torment her.
the fact that it 'could' be 'counted' as bullying means that it probably shouldn't be. sure, teasing can be taken to extremes, but what i have to go on, which is the article in question, describes teasing behavior (and some very accurate criticism of what is widely known as a horrible song), not bullying. in a world where a child can be prosecuted for bullying, it's very important to not throw around words that might have a harsher meaning than necessary.
so rebecca got tired of hearing people ask, 'what day is it?' and singing her song when she got close to them? welcome to the world of being well-known for something.