That sounds pretty unlucky to me, nearly new falkens shouldnt do that! as others have said, check tyre sizes, pressures and alignment, but to me it just sounds like you hit a slick of some kind. hope its sorted out ok!
Might be an idea to get some driver training if you havent been in rwd cars very long... firstly, because its an absolute hoot, and secondly cos it might just come in handy in these kind of situations... if you arent used to the back stepping out its easy to not correct enough, or to catch the slide, but then not know when to uncorrect, and go off in the other direction.
I know from when i first moved to rwd the feeling when the back steps out was entirely alien to me, but after a few training sessions it feels a lot less strange