According to Fox News, the makers of Soylent chose the name as a playful reference to Soylent Green, the well-known 70s sci-fi movie about human cannibalism. However, Soylent doesn't contain human meat.
Which is to say that Soylent is NOT a hoax or a joke. Even though it may sound like one. (I, for one, was confused for a while.) It's just a product with a weird name.
Whether Soylent will sell well, or end up going the way of other cannibalism-themed food products such as Hufu (human-flavored tofu) remains to be seen.