This is the power of data collection. This can be explained without mic's listening in, not that I think they aren't.
400 phones were all located in a bar at the same time, and a significant percentage of them googled 'LOTR run time' simultaneously. All 400 phones are now associated with a likely interest in LOTR movie. It's that simple.
Individual interaction with future LOTR test prompts confirms this association for their account and so on...
It is creepy how much data miners know about us whether we like it or not.