You are probably correct.
That said, this knowledge most likely included doing something to indicate he might be available to the senator.
I find it hard to believe otherwise.
After all, cops posing as prostitutes or drug dealers are actually doing things to encourage someone to make an offer. They bust those who offer money for sex or drugs.
So...what did this airport policman do to encourage Craig?
I think the only thing the UC did was just sitting in the stall. The Senator was caught as part of crackdown on lewd conduct at the airport. The Senator was not a specific target in the operation. Maybe the Senator had had some "luck" there on a previous visit, and this time, his intended pick-up happened to be an UC.
Again, "innocent until proven guilty" - and we have yet to hear the Senator's full story - but judging from the police report, it seems that the Senator was being a bit persistent. And if he did indeed block the front part of his stall with his bags, as well as put foot in the area of the stall next to him, well...
Of course, there were probably other people arrested in this operation, but since Mr. Craig happens to be a Senator, well...
*And when the police bust online pedophiles, the "child" is doing nothing either to encourage the predator except for posing as a child.