All that is happening is that the postfix + 10 and * 10 are being taken as arguments to be passed to the subroutine.

Kinda like the sub was declared with a ($) prototype:

use warnings;
use subs qw(non_commutative);

sub non_commutative {
    print "?@_?\n";
    return 17
}

$x = 10 * non_commutative;
$y = non_commutative * 10;

print "$x\n$y\n\n";

$x = 10 + non_commutative;
$y = non_commutative + 10;

print "$x\n$y\n";

__END__
c:\test>junk19
??
?*main::10?
170
17

??
?10?
27
17
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