How did Chevy come to these conclusions? Well, they assembled many groups of people and showed them pictures of the same guy. The only difference was the vehicle in the background, with one pic showing a badgeless, silver Toyota Corolla and the other showing the new Chevy Colorado.
The truck is red and the sedan is silver. The people are reacting to color and assigning the
positives to the truck. Reverse paint schemes and see what their reaction is. Ever heard of
a silver power tie ?
I'm also thinking that this is a poorly set up test. There are a lot of differences between the two besides "truck vs. car". Badgeless, different brands, different model years(!), different cost, different colors, and I think the picture of the truck is studio quality.
If you really wanted to prove that people prefer the impression of the pickup then you need to get rid of the variables. The Colorado starts at $21k, so let's pick a similar priced Chevy sedan. Looks like the closest one in price is the $22.5k Malibu. So if they pictured the guy instead with a red 2015 Chevy Malibu with the photo being of similar studio quality then you could call it a fair comparison.