Because this is the U.S. military, they took photos. Here, courtesy of the U.S. Air Force Dyess Air Base media page, is recorded evidence of this very American moment:
The idea of the test bombing run, explains Jacek Siminski of TheAviationist.com, is to demonstrate that the big bomber could be deployed against small sea-borne surface targets. Siminski cites pirates as a likely target, adding that "the term 'using a sledgehammer to crack a walnut' springs to mind." A single GBU-10 bomb costs $23,700. Here's a photo of the bomb impacting the (unoccupied) dummy pirate skiff:
If these photos don't make you jump up at your desk and chant "U-S-A" then, well, you're probably not a defense acquisitions contractor. Fun fact about the B-1B: It was developed in the 1980s for the Cold War, but was never actually used until 1998 against Iraq. Trying to adapt fancy Cold War weapons to a very different world is sort of an ongoing challenge for the military.
To be fair, it seems to me that the planners behind this exercise probably did not have Somali pirate motor-boaters in mind as the most likely target, but perhaps high-speed military boats like those Iran uses in the Persian Gulf. I'm not sure that makes a 2,000-pound laser-guided bomb strictly necessary, but it's at least a potentially more significant military threat.
(Hat tip to Dan Trombly for flagging this.)