Use your common sense please. The 9900K they are using there is overclocked to 5.1Ghz, it says right there. The 3900X is stock. The gap between the two at stock is 5%, hardly anything, and that's when gaming at 1080p and with a 2080 Ti. Not only does hardly anyone do this, out of all the people out there, few own a 2080 Ti too.
TechpowerUp tested with a large suite of games. It's funny, when AMD was losing bad, TPU were the go-to benchmarks. Now when the gap is tiny or margin of error, we got people quoting the amatuers over at Tom's Hardware!
Overclocking a 9900K, which is already power hungry and pushed to its limit, to 5Ghz on all cores results in massive heat and power draw, so it doesn't matter that it can overclock that high (and around 50% can't even get there without massive voltage), it's not a viable comparison.