(2-part post):
Let's start with the basic categories of assault charges. (e.g. common assault, ABH, GBH, etc). The appropriate charge is defined entirely by the nature of the injuries sustained, not by the method by which they were brought about. For example, you could simply shove someone but, if he was to fall into the path of a car, you could still be charged with 'GBH' if the resulting injuries were severe enough. (It would not be a defence to say " I only shoved him").
The injuries you describe most definitely fall into the 'GBH' category. (I'm very surprised that the police are considering using the alternative wording of 'wounding'. I suspect that the Crown Prosecution Service will amend this to 'grievous bodily harm'). The attacker seems to have admitted that these injuries resulted from his actions, so he's effectively admitted wounding or GBH. (As stated above, saying that he only threw a punch is not a defence. It's the nature of the injuries which are relevant, not how they came about).
However, when a charge of unlawful wounding or GBH is appropriate, the police and CPS are then required to examine the method by which the injuries arose, to see whether 'with intent' should be added to the charge. The deliberate selection of a weapon (such as a brick) counts as an indicator of 'intent'.