-bash: nethack: command not found
10.5.1

I think this game must be in a directory of some sort, or there's a command needed to open it.
Using my 1337 Unix skillz, I have determined that either your theory is somewhat flawed, or Captain Bob and I have some messed up computers.
Looking up "nethack" in Spotlight gives me two Unix "man" files: screen.1.html and zshparam.1.html, and these are in my "Developers" folders, which are only installed after installing Xcode etc. I suggest you look them up or try to figure out what you're doing, because as far as I can tell, there's no "nethack" on my computer.