Arbitrarily capitalizing letters is a typographic mistake: there are specific capitalization rules, and not following them is similar to having typos. So no, your colleague is not right.
If, for instance, your goal is to show the user that clicking on a button will remove all the cars, but not vehicles, keeping canoes, balloons, rockets and quadracycles unaffected, then you may simply add a hint which may disambiguate the consequences of the action. For instance, what about:
This rule will remove all the 283 cars (of 1.424 vehicles).
Another way is to actually show what would be removed. For instance:
This rule will remove the following cars:
[image1] [image2] [image3] [image4] show more
Finally, following Alan Cooper's Do, don't ask model, you can simply remove all the cars, and show the list of vehicles without the cars, while keeping an Undo action nearby. This approach is visually effective, as it makes it possible for the user to take an action, see immediately its consequences, and revert if this is not the action the user wanted to perform.
As a side note, I don't understand your “Continue?” If it's a confirmation dialog, you definitively need to read Alan Cooper's About Face, as well as my answer on a related subject.