Well, if we REALLY examine the picture a little more, you'll notice that the Z3 is the M version (wheels, vents, fenders). So, what is most likely happening here is the Scooby is just getting out of the way. You can see he is already making his way off the racing line, in preparation of the Bimmer zipping past inside.
When it comes down to it, it has more to do with the driver than the car. Last time I was at the track in my MINI JCW I spent all weekend lapping M3s and even double lapping some (and triple-lapped a Cooper S with a "JCW Killer" sticker in her window.
) The only car that kept up with me was a NSX. I had him in the corners and he made up for it down the front straight. I had downgraded myself from the advanced run group to the experienced group in order to learn my JCW (I had never tracked a FWD car before), so I did have an unfair advantage of experience over the field.
Cars aren't fast. Drivers are. Differences in cars don't really become apparent until you hit the advanced level of driver performance. It's always funny (or sad) to see novices come to the track bragging about all the mods they've done. In the end they suck, mostly because those mods get in the way of learning how to drive. I recently talked to a guy who was adding tens of thousands into modifying his E46 M3. I asked where he tracked his car and he responded that his car wasn't yet ready for the track. I bit my tongue, but he's going to look the fool on his first session if he ever gets to the track.
I tracked an E46 M3 for several years moving from the Novice/Intermediate group up to the Advanced run group. In that whole time my M3 stayed bone stock except for front brake pads (since street pads don't work well for track) and tires. My MINI JCW has upgraded tires, wheels, and pads. For the first time ever (after some 1000 miles of tracking) I finally added a power mod, a CAI and upgraded turbo hose to add about 20 HP.