The author's essay is interesting on that point. He freely admits that although his idea caught on in this context, there's nothing to prove that it hadn't been done before in other situations: "It's always possible that someone else had the same idea--it’s a simple and obvious idea, after all....Some people have told me that the :-) or :) convention was used by teletype operators in the old days. Maybe so. I haven’t seen any examples of this, but it’s plausible, given the limitations of the character set in that medium."
I'll vouch for that. As kids, we used to fiddle with typewriters to make "letter art."
Part of me finds it odd that "ascii art" was never experimented with prior to the computer. I mean, punctuation's been around forever, and even movable type has existed for several centuries. What gives?