Why TRUE not given to function in class

I have some issues with my large project, i cant figure out why TRUE not given into function.

I have:

class Cat
{
 public function abc ($a = FALSE)
    {
        if ($a)
        {
            print('YES');
        }
        else
        {
            print('NO');
        }
    }

    private function meow ()
    {

        $blabla = $this->abc(TRUE);
        //some code
}

It prints always NO

But this example in online redactor prints YES:

function abc ($a = FALSE)
    {
        if ($a)
        {
            print('YES');
        }
        else
        {
            print('NO');
        }
        }
abc(TRUE);