Isn't this all very simple? Someone did something wrong through poor judgement, got found out and now faces some appropriate sanction which the company is obliged and duty bound to deliver.
Secondary to this, people may well have a change of perspective regarding this "victims" own history of prior misconduct in the office. Seeing as this individual has opted to pursue this via the HR channel now others may feel that with the benefit of further perspective this is an option well worth considering themselves & make retrospective complaints about the persons past behaviour and personal comments relating to peoples anatomical attributes and sexuality - for which they surely deserve sanction themselves.
For the record and contrary to some previous commentary, WhatsApp is very decidedly a social media platform - Also it should be noted there's nothing "private" about WhatsApp's obliging nature in allowing one to forward images or video to 9 or 999 people outside of the original "private" group of addressees.
If you go around accusing people of poor behaviour you'd better be ready and willing to answer for your own.