He was an idiot for using his wifes phone if you ask me
True, but given the bug in the app, who would expect it?
As we know, separate phone and sim, no signing up to what's app, twitter, facebook, snapchat, instagram etc. Not even email. Texts and calls, traces of which can be quickly deleted or wiped. Plus have a passcode on that punting phone - and not an obvious one a partner will figure out.