Serious flood damage should be very obvious on a typical RV. That you see nothing at all suggests that it was not damaged in any way, presumably because it wasn't flooded. If it's been repaired so thoroughly that it looks as good as new, then it may well be better than new now.
I would not let the fact that the previous owner lived in an area that was flooded prevent me from buying a good RV. It sounds to me more like CarFax trying to prove it's worth the cost than anything. It's hard enough to find a good used RV that has no signs of water damage.