I can't speak for the previous poster but I can tell you that it is a near-zero possibility in my mind. It is hard to keep secrets and the cryptonote technology is incredibly interesting and important. I think gmaxwell (bitcoin core developer) described it here as one of the most significant developments since bitcoin (paraphrasing). Look at how quickly knowledge of Monero has spread throughout the bitcoin community and has become a "big thing."

If it had been out there being mined by thousands of people, word would have almost certainly gotten out, and due to the significance of the technology would have spread rapidly. Some random poster claimed on this thread to have heard about it, and that is actually credible in the sense that (hypothetically) with thousands of people involved others would have heard about it. What is not credible is word of this hugely significant technology not spreading widely.

Since I don't believe the claim of thousands of people keeping such a secret for two years, I view such claims as more evidence of deception and fraudulent intent.