When you find some random project on the 'net you should not immediately assume it is a well designed project. There is a whole lot of garbage out there. I see a bunch of stubs and “extra segments” in your screenshot. And although those are innocent in themselves, to me they are also an indication this was either a rush job, or the designer did not care much.
The red layer appears to be a continuous GND plane, and that is good. Having more GND is generally better ,but if the green / mint layer was intended as a gnd plane, then at least more clearance should have been used in between the tracks, so the plane can connect in between those tracks.
For a motor driver, it’s possible that on another part of the PCB the dual GND planes are used to lower the resistance of high current paths, and this corner is just given less attention. It’s also possible this PCB was designed by a beginner just experimenting a bit with how the software works.
Also, are you aware that you can create a PCB in KiCad by converting a set of Gerber files? I have written a tutorial for that in the link below.