Let's say you're in London. You hear this morning's news. You're upset not because of what's happened, but because you yourself weren't directly involved. So you quickly make up a story about an extra attack, that you witnessed, and you call the police or the BBC or anyone who'll listen and tell them all about it. How bloody inconsiderate are these terrorists, anyway? Don't they know how important you are? How dare they arrange things in such a way that events don't focus more attention on you?
For the record, only one bus has been destroyed and there was no suicide bomber shot dead at Canary Wharf. The people who "witnessed" these events should be locked up.