AFAIK, the primary objective of pilots when talking to passengers in situations like this is not to be 100% honest, but to avoid a panic. In this particular instance, he might also have tried to protect the flight attendant or avoid personal/company embarrassment. Although as a passenger, "I was accidentally pushed against the controls" would comfort me much, much more than "the controls of the entire aircraft suddenly went black and we have no idea why".
Guess the real reason may also provoke anger in some passengers. You can argue with attendants if you know that crew did it, you can't really argue with a plane or forces of nature. For those passengers providing fake reason would ensure a safe flight.
Because "oops, we almost just accidentally killed all of you" isn't a nice thing to hear mid-flight.