The man probably trusted his family, which is a really natural thing to do, though sometimes it turns out to be a mistake, like it clearly did in this here, as the son proved untrustworthy, unfortunately.
It is not about His trusting the Family but this is about the general case of the risk being hacked as he installed the wallet in His phone and at any chance can be hacked.
the point of this thread is to let people Know the risk of doing such thing and must be prevented .
I know as well if the Father had saved His funds in secure wallet like Trezor or Nano ledger .