Up until recently the PHP runtime was treating Groovy code just the same as Java. Anyone could compile a Groovy class to Java class files using the Groovy compiler. Those class files could then be dropped into a Zero application and used in PHP through the PHP/Java Bridge. The problem is that Groovy isn't the same as Java.
He compares the way its works when its Java-esque and how it should work as combined with the Groovy bridge. The code is much cleaner and, by making it more readable, makes it easier to maintain in the future. You can see some slides from a presentation hes given on the subject here.