The usual rule is multiple verifiable sources. If the same story appears in several places with several sources and I can trace the origins, then it is probably true. I've never been to Paris and have never confirmed personally that the Eiffel Tower actually exists, but I can find multiple sources that tell me that, that are verifiable. The odds of it being true are very very high.
On the other hand there is lots of lunacy out there that does not deserve to be replied to. Has any President ever denied that alien abductions are taking place? Has the White House spokesman ever denied that chem trails spray mind-control chemicals on the US population? Has the Air Force denied that they have a secret moon base on the far side of the moon? By your standard you have to accept those as fact since they haven't been officially denied.
If you really want an offical denial of the quote, call the White House (202-456-1414) and ask them about it. They will then deny it. Will that satisfy you?
Well, that's a good rule. Perhaps if the incident continues to be discussed additional information will be presented. Too quiet though, not even an official snicker at the thought.
They will then deny it. Will that satisfy you?
Would a "no comment" satisfy you?