Simple terminal graphics line drawing
Magic numbers

    0 constant X
    1 constant Y


looks more attractive than naked 0 and 1. I suppose (sorry can't test it right now) it may let you unify move-x with move-y, as well as reflects.
Height and width

    : height= h @ 1 - = ;
    : width=  w @ 1 - = ;


allow more symmetric definition of reflects:

    : reflect-top Y point @ 0=      dup  if  1 1 dir ! then invert ;
    : reflect-bot Y point @ height=      if -1 1 dir ! then ;


Now it looks like they have different stack effects, which is strange. Are you sure reflect-bot doesn't miss dup?
move-*

I'd rearrange pushes, e.g.

    : move-x 0 0 0 point @ dir @ + dup point ! ;
    : move-y 1 1 1 point @ dir @ + dup point ! ;


which really prompts for a point @ dir @ + dup point ! word. move-in-dir perhaps?
One screen

Do modern Forthers still care about screens?