When I played as the Dutch (or any other not-American civ) and you sent a caravel to SA, you might met an Incan galley (or scout or other unit). If you met the galley at least 1 turn before you can see the Incan borders, you don't get the free troops. Someting strange is: sometimes I sent a caravel and it can see an Incan galley but I didn't met them!
In my last 2 games I avoided the Europeans:
1) I had build a galley and it met a dutch caravel S of SA.
2) One of my 3 scouts (I get one from a goodie hut), explored the Rio De Janeiro-tile, and it saw a Viking caravel.