Just one problem - the flag was a spoof, displaying what might politely be termed "sex toys" against a black background.
No wonder Lucy Pawle, a CNN journalist, was the only person at the parade to worry.
In the since deleted clip, she said she was surprised that no-one else had reacted to the flag.
"This man dressed in black and white waving what appears to be a very bad mimicry of the Isis flag, but a clear attempt to mimic the Isis flag, the black and white flag with the distinctive lettering," she said, adding that she had alerted the police to its presence.
"It's clearly not Arabic. In fact, it looks like it could be gobbledygook," she added.
To his credit, Mr Bergen, who once met Osama bin Laden, tries to introduce a degree of scepticism suggesting the flag may be desigined to poke fun at Isis.
"It could be some kind of almost parody - it's possible," he said. "After all one of Isil's principal goals in territories it controls is to murder gays."
Inevitably the mix-up has been ridiculed on Twitter.
- Daily Telegraph
