Your definition of "sentient being" seems too anthropocentric to me. Why should anyone but humans happen to have evolved something like a brain with dopamine centers and the capacity for pleasure or addiction?
His position doesn't really change if you accept the use of "dopamine center" as a metaphor. For as far as we know, reward/punishment are essential triggers for adaptive neural networks. I don't think it's anthropocentric to presuppose that any advanced lifeform can artificially stimulate its own reward mechanisms.