The Pixel performs just fine in benchmarks. It doesn't score higher than every other Android phone, but it's in the ballpark of where we expect high-end phones to be.
And yet, when you actually use it, it certainly feels so much faster than every other Android phone you've ever used.
We can't explain exactly why, except to say that Google has probably spent a lot of time optimizing all parts of the Pixel's software stack. From touch latency to device drivers, cache sizes to polling rates, Google tweaked it all.
Android manufacturers, go and do likewise. Don't be satisfied with whatever libraries and drivers your SoC vendor (like Qualcomm), camera vendor (like Sony), or storage vendor gives you. Work with the OS, the firmware, the drivers, everything. Compile, test, measure, and re-compile.
Ultimately, we don't care that the phone we buy has the longest bar on a benchmark chart. We care that when we ask it to do something, it does it right away. That we can instantly switch apps, scroll smoothly through any page, and that all of our swipes, taps, pinches, and slides are met with instantaneous feedback.
Combined with a simple and elegant interface design, this is what makes the Pixel feel good. It's not the kind of "checkbox feature" you can easily market, but believe me, reviewers will take notice, and word-of-mouth from customers will be worth it.