grep doesn't search in strings, it searches arrays or lists. It makes no sense to use it on scalars. You give grep a list, and an operation to execute on each element of the list. For example:

my @list= (1,8,3,9,2);

my @newlist= grep $_<5, @list;

# @newlist would be (1,3,2);
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grep is sort of a loop and what you did was create a loop that always loops only once. So the following two lines are practically equivalent

unless ( grep $person_has eq $_,  $item ) {
unless ( $person_has eq $item ) {
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