It appears from (almost all) the lady AB'ers answering here, that the intention of a whistle is not always appreciated by the recipient.
Plus, I don't think this young lady went to the police because someone whistled at her - it was because she was feeling intimidated, which is an entirely different scenario.
I recall my fifteen-year-old daughter walking past a Kwik-Fit garage on the way to school and being called at by one particular lad, which upset and distressed her.
I advised the manager to have a word with the lad, and advise him that his comments were not appreciated, and ask him to please stop - which he did, and the harassment ceased.
I am quite sure that immature men in a 'group' situation often get a bit giddy and stupid, but that doesn't make it alright.