It appears to be a word made up to explain a rapid growth in AI due to the fact that such an intelligence can rewrite its source code and modify its hardware, whereas humans are relatively stuck with the limitations of our wetware. A take on the onomatapoetic word BOOM I think as it represents an explosion of intelligence/capability. By contrast, MOOF would be subverting the reward mechanism that underlies the FOOM growth, thereby resulting in a whimper (MOOF) rather than an explosion (FOOM).