It doesn't necessarily mean anyone bought the shares. The Market Makers maintain an inventory of the shares they trade and use that inventory to balance the trading in the security. Their inventory may go up or down while they adjust the bid/ask in hopes of maintaining that inventory. The bid/ask is simply the buy and sell quotes that they are willing to guarantee for a certain number of shares. While they can make some extra dough through commissions from large institutions, they mostly make their money from the spread and how well they manage that spread against their inventory.
News 
Market Data 
Discover 
