Wow! Some real red flags here! Children should not be asked to sit in time out and write as a punishment! Preschool writing should be a fun and engaging activity...not a punishment. I would be looking for another preschool! But before you do that...remember that it is a four year old that is providing you with this information. He might be seeing things a little differently than the adults do. I am not saying that he is lying to you...I just know as a teacher myself, sometimes kids do not convey information as it really happened. Their reality can be different than what the real reality of the situation is.
I would go in and just say you are concerned about his behavior...don't mention the other student. Ask them why they think this is happening, what seems to trigger the disruptive behavior, and see where the conversation goes from there. They might be seeing something that you are unaware of or missing. I would also ask the teachers what their recommendation is for next year.
If your child is not interested in the more "academic" side of things, it will probably do well to wait a year for kindergarten. As a kindergarten teacher I can tell you that kindergartens, at least the majority of ones I am familiar with, are very academic these days. A child who is not ready to sit for at least 15 minutes and attend to a story or task will suffer in kindergarten. It can be very stressful for children who are not ready to attend in class. He is telling you he is not ready by acting out, saying he hates school, and getting the negative attention that the other boy is getting. If he is showing these signs now it will probably continue into kindergarten, and then you are starting him off on the wrong foot. It will be hard to change his attitude towards school if it starts out bad.
I would find another fun, hands-on, engaging preschool that encourages children to learn through play.