The version that played against Fan Hui was reportedly trained that way, but if I recall correctly the more recent one that played Lee Sedol did't rely on self-play as much.

Also the objective was different - they tried to train a network that would play well against any opponent. It should be easier to train a network that exploits some very narrow weakness in specific AlphaGo version.

For example, my phone consistently beats me at chess. But I found a sequence of moves in one opening where is always makes the same mistake, and I after that I can win easily.