When I go to join a multiplayer game in Starcraft 2, sometimes the game client says it is downloading a few items before it enters the queue. This notice appears at the top center of the screen, and is soon replaced by the the "looking for players" message and then the "players found" message.

What is it downloading? Presumably I already have all the game content, and also presumably it can't fetch data on my opponents (such as their avatars) until it has decided who to match me with, which can be minutes later. Blizzard isn't issuing micro-patches this way, are they?