OTC buyer? That's very unlikely. He's obviously a miner because he's receiving 50 BTC-transactions. The first transaction happened on February 5, 2009. That's not less than a month since launch because Bitcoin was launched on January 3, 2009, that was when Satoshi mined the genesis block. That's a little more than a month.
Was there even a way to buy Bitcoin over the counter at that time? And with how easy to mine Bitcoin back then, people would just do it rather than look for a seller.