Here's why ...
Paint manufacturers come up with their formulas for the "standard" color provided to them by the auto manufacturers. This means each manufacturers paint may vary.
Auto manufacturers use "2nd tier" manufacturers to make everything plastic on the vehicles ... mirrors, door handles, bumper covers, trim pieces, etc. Those manufacturers paint the parts based on the standard.
The auto manufacturer might get a deal on a train load of paint from Dupont. One second tier manufacture might be shooting Sherwin-Williams. Another second tier manufacturer might be shooting PPG. At any point during the year, each of them might buy paint from another manufacture. All the paint is the same paint code, but may vary slightly, or significantly, between different brands.
Add to that, paint shot over plastic will often look different than the same paint shot over metal, and the color of the primary might vary and effect the final color. How it is applied (for example, how thick it is applied) can effect the color. How fast it is applied (as in dry time) can effect the color. At the auto manufacturer, paint is often moved through pipes over very long distances. Metallics slamming into the 90° corners of those pipes can break down and become smaller. Silvers and whites generally have a large number of alternates, some which are significantly different from the standard ...
In the end, you can easily end up with several versions of the same color on one vehicle.
On your truck, there is heavy mottling on the bumper cover. That means they set up the paint to dry too fast so the metallics didn't have enough time to lay out. The paint on the body looks much better. The mottling is playing a big roll there in making the colors look different.