I failed to follow how author introduced "attacker" to this story, when there are no visible suggestions, only his own old credit cards on file, to which he did

I failed to follow how author introduced "attacker" to this story, when there are no visible suggestions, only his own old credit cards on file, to which he didn't incur any charges and all that must have happened due to routing mistake crediting someone's funds to his account. Something which must have been rectified very quickly even without author noticing.