It is not, in fact, random, from what I've seen. The only time I couldn't predict what the fact would be was when I did not hit any combos.
Every time you complete a game (I just kept playing the Challenges one after another, switching off with my sister when my arms died), and whether you win or lose a fact will come up at the end about one of the fruits.
From what I've played, the fact will be about the fruit that appears most in your Best Combo.
So if you have a 6 fruit combo, and you got 3 limes, a watermelon, and 2 lemons, your fact would be in reference to the Lime.
Best way to win this is to just keep playing for combos (Zen works best, unless you don't mind the bombs in Arcade mode). If you just need one more fruit, try making that your best combo.