Because you're effectively using a hash slice.

What that does is the @ in front of the hash presents its keys. Then if any of the keys match any elements in the array, those values are returned:

my %h = (1 => 'a', 2 => 'b', 3 => 'c');
my @a = (2, 3);

my @b = @h{@a};

print "$_\n" for @b;

__END__
b
c
[download]

-stevieb