If there was any movement in Alphabet, it should've been in January when the news came out. Markets don't move on anticipated events but unexpected events, and judging from the various betting markets an Alphago victory was not that surprising; the victory also didn't mean much because the widely held opinion was that Alphago can be expected to improve steadily over time and so even if Lee Sedol won, he would lose in the coming months (I believe Sedol said something like that before the games started, and Ke Jie has also revised his earlier comments and is now saying that he would lose to Alphago in a few months too), in which case the meaning of the match is reduced to a slight shift in the improvement rate - along the lines of 'Alphago didn't improve quite as fast as Deepmind expected'. Which is not something which is meaningful to Google's bottom line.

(The real point of the match was to prove a point to the muggles and AI-deniers and get good publicity, of course.)

It is not a good proxy. Deepmind is a small team and there are many more teams within Alphabet doing machine learning. Remember that the market cap of Goog is $500 billion. (Although if one wants to invest in AI in general I think it is a cheap stock)