He was charged - a lot of people are charged because it's "in the public interest" for the circumstances to be aired in the open, when there is a question of if a law has been broken.
The fact that he's been found not guilty means that in the eyes of the law he was innocent (probably based at least partly on the self defence grounds that apply to anyone - you're allowed to use reasonable force if you have a reasonable fear for your safety).
As for the "it was just a carton and mobile phone" argument, people can and do disguise weapons as every day objects (at the extreme end of the argument there are I believe guns disguised as mobiles, and it's pretty easy to say put something solid into a container making it into a cosh/club), he had seconds to see, identify and take action on a possible threat to his/his colleagues safety in a very hectic environment - he did so following the training he had received to protect himself using minimum force (warning, slap, then baton to relatively safe part of the body).
Personally I thought it telling the women sold her story to the papers (didn't mind the publicity when it was paying her), but then didn't want to appear in court because of publicity about her life that might have came out.
The sad thing is, that even though he's been found not guilty in the courts, he's still likely to be investigated and possibly punished by the Police services own regulatory/punishment body.