All magic in PHP starts with __. Lets see if I can find a link for that. Ah, here it is: http://www.php.net/manual/en/userlandnaming.rules.php
condition is not a valid pre-defined constant. Either it was set as constant prior within script, or you simply did not have your error reporting set highly enough. If condition is not declared, it will trigger E_NOTICE and return true, since the string 'condition' is true.
So if its not a valid defined constant, than you've been returning true regardless of if it should have been or not.