I wrote a disassembler as part of my own Chip8 IDE[1]
It doesn't look like it impacts this disassembler, but it's worth noting that Cowgod's Chip8 technical reference gets the shift and load/store instructions wrong. A much better reference is Mastering Chip8[2].
[1] https://github.com/JohnEarnest/Octo
[2] http://mattmik.com/chip8.html