Bob might be working his ass off to improve bitcoin, which in turn raises the price of bitcoin. But Joe sits back and enjoys the fruits of Bob's labor by simple holding on to a bunch of bitcoins he did almost no work to acquire.
Bob probably owned bitcoins prior to Joe, and Joe's purchase of the bitcoins took them off the market which decreased the supply of bitcoins for sale and possibly helped to cause the exchange rate to rise.
The gains in the exchange rate either motivated Bob to continue his work or he may have even took some profits and sold at a higher rate, using the gains as bootstrap capital to help fund his endeavor.
i.e., that's not communism.