Biomecanoid

I took my old 2006 Daihatsu Sirion to be inspected a few months ago as it is required where i live every 2 years. I have no problems with the car works fine and it was my 1st inspection since i got it. When i took it to the garage to be inspected the guy there did what he was supposed to do but when it was time to do the emission test, he pressed the gas revving the car and a cloud of white smoke came out the back ( My car has never done this before never ever have i seen and smoke coming out of the exhaust and i live in a hot climate so no condensation to blame ) then he asked me to go to the side with him and told me that my car does not pass the emissions test but its OK he can let me pass, i guess that was his cue to give him money LOL, i didn't and the car passed the inspection. Now my question is could the mechanic at the garage put something in the exhaust to make the car smoke temporarily just to put on a show and get some quick cash ?