The gm's do a very good job. I've worked with them on several occasions. They wouldn't have banned your friend without just cause. What you see in FC chat and what they tell you, doesn't necessarily include anything like tells, which is probably what got them banned. They don't just get a complaint and swing the ban hammer. They do a detailed investigation. I've even had to include timestamps in my supporting evidence before. You're friend got banned for a reason.

Remember, you as a player agreed to SE's terms of service which clearly state that harassment will not be tolerated. First occurance results in a warning, second is a 3 day ban, further occurance can mean a permanent ban.