libvpx, the VP9 encoder library used in this test, has no support for any hardware encoder blocks for VP9 [1], so it does everything in software. There are ways [2] to compile some support into ffmpeg-with-libvpx that makes it able to invoke the hardware encoder in newer Intel CPUs (Skylake or newer) [3][4] (using vp9_vaapi) but it's doubtful that this was used, since their command-line switches indicate nothing of the sort.

x264 is a software-only encoder that provides no hooks into hardware acceleration. Their ffmpeg command line indicates that no hardware acceleration hooks of ffmpeg were used.

[1] https://github.com/webmproject/libvpx/blob/master/CHANGELOG [2] https://gist.github.com/Brainiarc7/24de2edef08866c3040805048... [3] https://cgit.freedesktop.org/libva/commit/?id=fb57f5c15e72c3... [4] https://en.wikipedia.org/wiki/VP9#Hardware_implementations