Chris Sutton said the same on MOTD2. It was an accident so the red card should be rescinded!! I will accept that it wasn't intentional but Mane knew the keeper was coming and should have pulled out. Why didn't he go for it with his head as well? Players have a duty of care to their fellow professionals and Mane was reckless and out of control.
If it was intentional, he would be going to prison. If you intentionally run and kick someone in the face resulting in them requiring urgent medical attention you'd get sent down.
It was unintentional clearly, but just as clear it was dangerous play.