If it's unauthorized access, than it doesn't matter who accessed - family, neighbor, boss, employee - unauthorized is unauthorized and Reg E applies - period!
Now, the only thing that may have happened that I can think might cause a financial institution to make that comment is if the unauthorized access came about via an access card that the customer gave to the family member to make a purchase, along with their PIN. That situation could cause a bank to deny the claim.
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My comments are absolutely no reflection of, nor influenced by, my employer - take them at your own risk.