No, the size should be 2 because your hash has 2 elements: a key and a value. The hash is expanded into a list when pushed onto an array so the array has 2 new values, the first being the key and the second being the value. eg:

#!/usr/bin/env perl 
use strict;
use warnings;
use Test::More tests => 1;
my %z = ( a => 'b' );
my @x = ( 'a', 'b' );
my @y = ();
push @y, %z;
is_deeply (\@x, \@y);
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If you don't want the hash expanded in this way then you must use a reference to it instead when you push it. The reference is then just one element in the resulting array. It will probably help you greatly to have a thorough read of perldsc.