From what I've read, the flyby wasn't a surprise. The altitude was. Nobody expected a B-52 to fly below the level of the flight deck...other than the crew of the BUFF.
Also, although the B-52 looks like it's pointed downward, they just fly nose-low. A quirk of the design.
My Uncle was a radio operator on a B-24 in Italy. After recording his WWII story, I did some searching for pictures. This is his B-24 "Dinah Might" that crashed on landing. He had rotated home before the crash.