[Cheburashka]

He’s was probably smart enough to figure out the clerk was testing the money, so why didn’t he grab it back before it was tested, since he knew it was fake? Answer: he didn’t know it was fake until it was tested.

You admit you would have done what he did if you thought about it, so why be surprised he did exactly what you would have wanted to do?

I don’t know what they call the agency that handles Presidential security, but I bet this will be a source of merriment to everybody until hell freezes over. “Hey remember when Boris tried to buy booze in America with American currency and it was counterfeit?”

[Brainhose]

"He’s was probably smart enough to figure out the clerk was testing the money"
Odds are that this Ruskie had never been to a NH State liquor store. And it also stands to figure that he did not see any bills being tested since as a rule only $100's are checked. So, by the time the bill was being tested it was too late and he grabbed the bill and scooted. Believe it or not but it's not incredibly common to see $100's bandied about which they wouldn't know as they no doubt are lead to believe that all Americans are inferior.
"I don’t know what they call the agency that handles Presidential security."
If by "They" you mean Americans, we call them the Secret Service. I'm not sure what you guys call yours