That aceable.com description is perhaps the worst definition of yaw I've ever read. The wikipedia definition is much more accurate:
https://en.wikipedia.org/wiki/Yaw_(rotation)
As SamPedro describes in his 2nd post, yaw isn't always a spin, it's just a turning motion -- anytime the vehicle rotates at all about the z (vertical) axis, that's yaw. If you drive in a complete circle, you've completed 360 degrees of yaw, regardless of the radius of the turn -- a freeway ramp, a parking lot, or a donut.
Anyway, I would suspect the alignment is a likely cause, either too much toe-in or toe-out on the wheel hitting the bump or pothole. If the PSM were doing anything to cause or correct the yaw, I think you'd get a flashing light on the dash during the PSM activation.
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