Maybe it was a bit strongly worded to say that Christian evangelism is forbidden, but it is restricted. Notice also that I said "de facto". It's not law, at least not in most cases, but there are restrictions put on Christian speech. For example, when I was a teenager, there was a Christian Bible study group in my high school that met once a week before school started. That isn't allowed any more. Many students brought their Bibles with them to school back then, but more recently, kids have been suspended or even expelled for bringing a Bible to school. Saying grace before eating in the cafeteria didn't used to be a problem, but I recently heard of a second grader being told it was bad to pray and being prevented from praying before eating. I've also heard of high school students being threatened with suspension if they said grace in the cafeteria. (From what I recall, praying for the cafeteria food is probably not a bad idea.)