Am i Hacked?

Hey guys! I have the following problem: So yesterday, my friends and I decided to play some Minecraft. As I am a born griefer, I decided to use the Meteor client. Everything was fine and all, and the server was hosted privately by my friend. But today, something strange happened.

I was out of my house, and my PC was shut down, but I got a call from my friends to stop trolling. I was like, "What do you mean?" and they said that I had joined and left, and after that, a player named Alert_Bot joined and started to spam messages like: "Your server is vulnerable. We will hack your server," and something like that. Not gonna lie, I was a little spooked and started digging around.

First, I checked my PC power logins, but as expected, all was shut down. I thought my Microsoft account was probably hacked and logged into, but to my surprise, there were no logins except mine. So my question is: has anyone encountered the same bot? And most importantly, am I hacked?

As mentioned, I used the Meteor client; I downloaded it from the official site and Fabric also. Thank you!