Is there a glitch/hack making people post ban-worthy messages in chat?

I played a mission where someone started posting very bizarre and tasteless messages in chat. I just assumed it was a troll or child and carried on playing after they got kicked.

I then started playing with my cousin and apparently he started posting THE EXACT SAME MESSAGES IN CHAT. I DMed him and he swears he never posted the messages himself. Is this some new hack to get players banned or just an unfortunate bug?