That isn't quite correct. The police firstly have a discretion as to whether to press charges, depending on the nature of the evidence and the seriousness of the charges. Secondly, while the technical ingredients of the charge can be satisfied the court may also decide the offence doesn't warrant serious penalty, particularly if there are mitigating factors involved. The charges could even be dismissed.
It is technically an assault simply to touch someone else without their consent, but you won't see charges laid. (It is also technically an assault without a blow being landed - if the victim has a reasonable fear they will be struck.) You may think it is "mental gymnastics" but legal matters are very rarely black and white (and I say that as one whose professional training was in law).
In this case I could well see a court taking the view that the offence was at the minor end of the spectrum - a lawyer could easily argue it as such. The penalty is unlikely to match the highly publicised indignation of the reporter and those who choose to characterise the offence as an outrage.
But we have entered the realm here of sexual politics, where values and beliefs - and who you stand with - define the issues rather than the facts. The polarisation of opinion on a site such as this demonstrates this. Yet if a matter involving a proven sexual violation had occurred - in common parlance, a rape - I would expect the consensus to be overwhelmingly for the victim. By trying to categorise lesser forms of conduct as serious that consensus is lost in the political shouting that takes over.