On the information you've given, I wouldn't think there's a chance in hell that he would be jailed.
Far more likely to be a fine, especially if he pleads guilty(as long as he is guilty, that is).
It's likely to be a costly experience, however. He would undoubtedly find that, if convicted, not only would he have to pay for damage to the Porsche, he could be ordered to pay Court costs which could easily run into hundreds in Mag. Court.
It's more likely to be dealt with in Mag. Court which does have limited sentencing powers but could deal with this matter.
He must have had legal advice at the Police Station. Get him to contact whoever that was for further advice.
He may qualify for Legal Aid.
Good luck.