1. It doesn't show off the unique capabilities of firecracker very well.
2. The comparison not very fair.
2a. The docker-build step (which dominates the runtime) is run without any caching, just by adding 2 lines to your build-push-action, "cache-from: type=gha, cache-to: type=gha,mode=max" you can make it a lot faster.
2b. ~1m20s of the time is just "VM start". GitHub Actions has had a rough time recently, but you should never wait that long to get your CI running in day-to-day operation.
2c. The tests are unrealistically short at 20s which allows the author to get to their 10x faster number.
Let's say the GitHub Action starts in 5 seconds, the GitHub Actions cache reduces the build time to 2 minutes and the tests take 10 minutes to run. Now Firecracker is 20% faster ...
You can also get comparable performance out of https://buildkite.com/ which lets you self-host runners on AWS meaning you're almost guaranteed to get a hot docker cache (running against locally attached SSDs). You can now start running your tests (almost) as fast with much more mature tooling.