The title is a bit misleading; it's running on an 8088-compatible CPU, and a 1 megabyte SRAM, with the FPGA containing the display adapter and drive controller, as well as the glue logic.
This build demonstrate what’s actually interesting about FPGA to me. A pure implementation might as well be a software emulator. Being able to interface real chips makes this really neat.
The author used the lattice fpga for exactly what it was designed for: glue logic. This fpga type isn't what you'd throw a couple of cpu cores on, it's more along the lines of replacing a few dozen 74xx series logic chips. I personally enjoyed the author using modern day chip equivalents instead of soft cores on an fpga. I find the latter to be much less interesting.