All life is only a set of pictures in the brain, among which there is no difference betwixt those born of real things and those born of inward dreamings, and no cause to value the one above the other.
Some of the Counteraction chits use the word chosen in a peculiar way. For example: "If the chosen AI is hit: Rally."
There can be up to 3 Counteraction chits in a row (#1, #2, #3). Let's say this message comes up in Chit #2. Sometimes Chit #1 specified a Unit or AI that then we can assume is the "chosen" one. Other times, though, there's nothing in Chit #1 like that, and I'm left wondering what the heck "chosen" means.
I don't have the game yet but just read the rules. In their example for chit #16, the word "chosen" referred to the text on card #16. I assume each chit refers to the card that invoked it.
For your example of chit #2, a look at card #2 reveals this:
Card #2 wrote:
Victory Points: Defend
Place a Soviet Control Marker at least 6 hexes from the Soviet entry edge. Place a card’s Units on the map.
I would think the units you chose to place on the map per this card's instruction are the chosen units referred to on chit #2.