You apparently insulted them through the chat. It's pretty hard to detect sarcasm or joking around in the way you were doing it in a chat box. I'm not saying you were the worst person in the world for saying that, but apparently they took it differently than you meant it. They may be a little sensitive, but they have a lot of people actually making fun of them throughout the day. They may just have been having a bad day. Sorry you got banned, but it is their channel, and they have the rights to do whatever they want on their channel

You are completely right, unless the streamer is being sarcastic, they can't tell. Honestly I think people should try a new approach and be nice maybe to streamers.