I know all company's can monitor, but he has said his employer, not the IT guy. plus he has now said around 10 people are aware of it and gossip... so it sounds less of monitoring and more of a direct attack on a user with some cort of tool. So the boss may be an *** and wanted to pick on him..
who do you think these companies are if not the employer?
first the IT guy? - who do you think that IT guy works for? uuuuh the employer?
and why do you think the employer/company pays the IT guys??
so IT guy is necessarily party to the information, the employer wants and can get the information.
and you'll have most likely signed a waiver to say that you're happy with that when you started, you;ll have most likely clicked OK I AGREE every day before you logon.
There are no limits on who this data can be shared with. (well technically there are, but actions for joining groups. - unless the nature of the groups was sensitive would not matter.
sounds like whatsapp was the only thing of interest.It sounds like its just whatsapp and not all traffic, so must have some sort of app that can see a users activity (I know facebook use to have one until they shut it down).
Actually it sounds more like the OP was dicking about in work time. and probably has been for a while and it's gotten to the point that his employer is watching him now and exclaiming loudly now he;s joining groups, (presumably rather than actually doing his work!) - so less a everyone gangs up on the poor innocent guy and more, work shy guy who consistently lets his work slide and plays on phone is soon to be shown the door.
So far as the legality goes.
if they use traffic capture and packet analysis to see what he's doing on the network then that's fine.
if they shoulder surfed or key logged a password then logged in as him at another time without him knowing so that they could watch his whatsapp account, silently receiving messages in parallel to him, without his authorization. then that is illegal.
not that it matters... - it only matters about it being illegal if you can prove it an intend to pursue it.