Google is at a trade show - this is not a public space. The show is in a building and that is private space. Any vendor is within their rights not to be photographed on private property. This is not happening in a public space.

The man pictured on left declared that Google PR doesn't want photos taken
of their booth and told me I must vacate the area. I politely told him
I had every right to take a photo, to which he said he understood, but
was being forced by PR to make the effort to avoid people taking
photos. What didn't they want you to see?