Strange php if behaviour with casted to boolean int

let's see if somebody can help me.

I have function called ret_error() which is called when there's an error accessing a table in a database, that means, "could not connect", "record not found" and this like that. This functions returns an array with two keys like this

array('error' => true, 'code' => Model::RECORD_NOT_FOUND);

If I call a function that returns an array built with ret_error() and I inspect the array it is like

$result = array('error' => 1, 'code' => Model::RECORD_NOT_FOUND);

But when I evaluate with an 'if'

if (!$result['error']) {
   do something;
}
else {
   do something else;
}

Always is evaluated as false even if I cast to a boolean.

This works correctly if evaluated as int such as

if ($result['error'] != 1) {

Is there something I'm missing?.