Rippling happens in tufted carpets. There is a scientific explanation which I can't quote precisely, but it is something to do with moisture affecting the different materials in different ways so the tension across the carpet is disturbed. Differences between the primary/secondary backings, or something to do with the latex. I can't remember exactly.
Yes a BW will ruck with dimensional change, but that is a totally different thing. It probably wasn't fitted correctly, a bit too slack maybe. If it was fitted properly, a small amount of desire to shrink should just pull up tension on the grippers (which should be doubled up, tacked and glued to the floor) and then dissipate as the carpet dries out.
To date I've never seen a BW installed correctly.