Leona Lewis Slapped At Her Book Signing

So today Leona was in London signing her new autobiography 'Dreams' at a Waterstones like I mentioned yesterday and it has been reported that she was slapped by a man.....

"We were called to Waterstones Piccadilly Circus at 4:35pm to reports of an assault.It appears that a male has slapped a female at the location." said a Scotland Yard representative

I'm sure more details will be released soon.

What I want to know is why?

UPDATE

A statement has been issued:
“Leona was the victim of an unprovoked attack this afternoon at her book signing. The police were called immediately and medical attention has been sought. Leona is understandably shaken and apologises to the fans she was unable to meet and complete signings.”

Thanks to Punchbowl Blog for the update