That's a pretty cool project. Sure you CAN do it in any language (as another commenter points out, you can do it in C too). Anything that's turing-complete can do it. You could also use C to parse ASCII art and have that create a TCP implementation. It's not the natural way you'd do it in that language, though.

lapp has been around for four years; docopt is (looking at git commits) less than a year old. It strikes me as a natural way to do things in Lua, which is why (I suspect) it was done in Lua earlier.

It can even be done in static languages with an intermediate compilation step.