Some kids, just do not know social protocol, and do not have impulse control per assessing situations. Hence they get in trouble. Or they do know the rules and about manners, but don't do it anyway.
I work at my kids' school, I see kids like this. No they are not a "bully", but they continually push the envelope and even disregard adults and the other kids, and just do what THEY want, anyway. Even if it is a disruption.
So this is not good.
Sure a kid has their own opinion. Fine. But a child, needs to learn, the appropriateness, about it, especially in school.
My kids are very opinionated, regardless of their star sign... but they are not disrespectful.
In any grade, at any age, a child has a Teacher. There will always be personality differences... not only between child and teacher but also between child and other classmates.
It is a life lesson.... and a lesson on socialization and how to manage themselves, in the bigger picture.
I would think, that your son, perhaps, is also affecting the other kids. Meaning, if he is disruptive like this as his Teacher says, then it must be evident to other kids, too. Most kids, KNOW what kid is disruptive or not, in their class.
If your child is also affecting other kids, due to his behavior, then the Teacher MUST address it.
"Yelling" is also subjective. Some people, child or adults, think any loud voice is "yelling." When in fact, it is not. And Teachers do need to be "strict." Meaning, they must make sure their kids are listening, doing what they are supposed to, and meeting the school's rules, too.
A Teacher is not there to be a buddy.
I think you should also attend the meeting, so you can hear first hand, what is going on.
And just because he is a Libra, is does not mean he can act that way.
If life were like that, then everyone would have an excuse to be and act the way they want, blaming it on their star sign. As though they have no ability to control, their own actions.
Receiving more than a handful of notes about his behavior in 1 month, is significant.
He must also learn.... to be responsible over his own behavior or upon others.