I also think you did the best thing. I think how we handle this sort of thing depends very much on the kid vs. always saying it's best to say nothing.
If a kid is asking questions, no matter his/her age, they know something is up. Pretending nothing is wrong only teaches the kid not to bother asking you about future issues. And as they do know some thing is wrong it can teach them to second guess their instincts where in reality the situation calls for validation. Someday they will put the pieces together and they'll remember how it was handled when they did ask questions.
None of us wished this for our kids. But skirting questions and pretending things didn't happen can do them a great disservice.
I think it's best to answer honestly with tact, just as you did.
Me 41, H 47, M 15 yrs, S11, S13 BD 1: 11/4/14 we work on it; really I pretzel myself BD 2: 3/31/15 H goes down to "dorm room" 8/15: H back to MBR 10/15: H back in dorm room 1/18: H files, now divorced