Valve does a lot of data mining on their own, and I wouldn't be surprised if Steam was sending them a crash dump directly, possibly with the last actions you were doing and the most recent save game. If multiple people were hitting it, the crash probably was at the top of a report, and above the "flakey machine or other unfixable by us problem" threshold. I used to do similar checks on crash dumps for the live game I worked on, as it is one of the best ways to ensure that the bugs being fixed are the ones directly impacting a lot of customers.

http://steampowered.com/status/ep2/ep2_stats.php has the info they make public, including maps of each levels with data on where people are dying.