I think Clinton was active with the British antiwar movement in the 1968/1969 timeframe, IIRC. There were quite a few antiwar people who made trips to Moscow (often entering via Scandinavia) during this period.
For US Senators, there was an overt reason to go (in addition, there may have been covert reasons, of course).
But for a footloose college boy to be hosted behind the Iron Curtain, months after the tanks rolled into Prague, would have been very, very unusual.
There had to be more to the story.