Isn't the world's supposed to be drug tested?
yes, they have random tests of some of the top five in each class at the IFBB Worlds. There are 8 weight classes, and that year 4 of the top 40 were DQed. So either Dennis passed the test, or more likely was not tested.
The winner of the middleweight class, Arturo Casteneda, did fail the drug test. Here is a video from that same year.
The funny thing is that Arturo has failed his drug test each of the three times he's entered the Worlds: 2000 1st place lightweight, 2003 2nd place welterweight, 2005 1st place middleweight. In 2008 he won his class at the Arnold Amateur.
BTW, the IFBB rules for the Worlds don't say "pass the drug test the day of the contest", but "three years drug free".