By way of explanation:

my ($date)
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provides a 'list context'. In other words, $date is part of a list of variables, where the list happens to be of length 1. That list of variables expects to be assigned a list of values. In response to that demand, the match operator m/// returns a list of of the actual matches to the parenthesized groupings in the regex.

If m/// happened to return more than one value, because there were multiple parenthesized groupings in the regex, then the rules of list assignment would take over: extra values on the right hand side of a list assignment are discarded. Here is an example:

use strict;
use warnings;
use 5.010;

my ($a, $b) = (1, 2, 3);
say $a;    #1
say $b;    #2
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