PIK is building on guetzli and butteraugli, gives about -55 % less bytes than JPEG for the same butteraugli score. Decoding speed is 2/3 that of JPEG. Encoding speed is impractically slow in this version. PIK aims at delivering very high quality photographs with minimal bandwidth and decoding (cpu and memory) costs.
Yes, you would have to read the source code. My guess reading the README.md is that due to the dependencies in the README.md its a JPEG competitor that is fast due to HEVC. The README.md even says this is still experimental. This project really looks too immature to be posted on HN without a technical breakdown. (This is not to disparage the software but for people to remain interested there would have to be at least some benchmark and it would be nice with a visual comparison).