I would imagine it's something that worked at the time, because it successfully exploited the slow, static movement of his opponents, but today it's probably "p

I would imagine it's something that worked at the time, because it successfully exploited the slow, static movement of his opponents, but today it's probably "priced in" as a possibility with known correct countering, so that people don't actually use it anymore. Like a rare chess opening that was once used successfully until people figured out how to deal with it later in the game.