It's YouTube. This is the place where you'll see a guy appear to pull an orange out of a book, or pour milk into a TV screen. That's the magic of video editing, you can't always trust what your eyes can see.
That being said, 20 FPS is very low for that system.
https://www.techspot.com/review/712-arma-3-benchmarks/page5.html
It may not be well-optimized, but when Techspot tested with the 700 series-based Titan (roughly comparable to your GTX 970, http://www.tomshardware.com/reviews/gpu-hierarchy,4388.html), they had no trouble getting more than twice your FPS with even 1st-gen Core i7 CPUs & AMD FX-series CPUs -- & most of the Core i5/i7 & FX CPUs were well within a few FPS of each other.
Have you checked your CPU & GPU temps when running the game to make sure they're not spiking? Did you also make sure you have the latest drivers for your GPU? And did you check to make sure nothing else is running, & that you're running in fullscreen vs. windowed mode? Finally, what are you using to measure your FPS?