The people going "ton of bricks" are being ridiculous.
Not at all. OP's son was harassing a man and then assaulted him.
Op took his phone and entertainment away, he is grounded, she let his school and head of year know, she gave him "the speech" . What else could she reasonably do to not be seen as lenient?
Come down on him like a ton of bricks. OP said her son was 'Basically up to no good', she needs to see her DS harassed a man and then assaulted him. The dire consequences that could have occurred for the man he assaulted and for her son needs to be clearly spelt out.
He fucked up. He broke the law. He assaulted a man. The police is dealing with it(rightly or wrongly) , his mum is dealing with it. She's angry and disappointed and worried. She probably needs some support to navigate the complete mindfuck and shock that this is.
Hence people saying come down like ton of bricks. Separate him from these so called 'friends', find out if he feels any remorse at all, find out what actually happened for that matter.
OP must be going through an awful time but minimising what her son did doesn't help anyone. Admission of the scale of the issue is the first step in trying to sort it.