\d matches more than just digits

utf8num.pl

#!/usr/bin/perl

use strict;
use warnings;
use open qw( :std :utf8 );

# http://www.fileformat.info/info/unicode/char/06f3/index.htm
# Unicode Character 'EXTENDED ARABIC-INDIC DIGIT THREE' (U+06F3)

printf( STDOUT "%s: %s: * 1024 = %d\n", m!\A\d+\z! ? "num" : "nonum", $_, $_ * 1024 )
        for "1", "foo", "\x{6f3}"
;

__END__

$ perl utf8num.pl
num: 1: * 1024 = 1024
Argument "foo" isn't numeric in multiplication (*) at utf8num.pl line 8.
nonum: foo: * 1024 = 0
Argument "\x{6f3}" isn't numeric in multiplication (*) at utf8num.pl line 8.
num: ۳: * 1024 = 0