Wavy tires?

Recently heard some "thud-thud-thud" noises coming from the rear tire of my 2006 Honda Civic. I immediately thought it was something embedded in the tread, hitting the road at regular intervals.
I put the car on jacks and took the wheel out. I've seen tire feathering, I've seen camber wear and the usual inflation related wear too. But wavy surface?!? There was no sign of "wear" where the area of the tire in question looks worn. Instead, the tire looks fine, just the surface isn't perfectly round.





Has anyone seen this??? The tire has been replaced since but I'm still not sure what happened.