This kind of major decision would have been made with the full agreement of the board. They have some very impressive investors, including DFJ, Union Square, and A16Z. The theory that all of these people, people who collectively happened to have $160m on the line, just happened to miss easy monetization opportunities is implausible.
I don't think that follows. People and organisations make mistakes all the time; it's equally possible that Foursquare made a bad decision here.