Oil canning is a relative word and so is wavy. They can be natural or caused by welding or grinding heat. I don't know how much or large of a patch was done. You can see all the effort was done, with the large dimples the factory put in, to elimimate oil canning. Very common in sheet metal design. Any change in direction of the metal will stiffen. Dimples, corners, flanges, indentations, a bracket, etc. Looking at all the changes in direction in the areas you show, I don't believe you did anything to cause that unless you did not cool or go slow during welding.
Sounds like you can live with wavy. It's not the only "wavy" place on the truck I suspect. If it actually oil cans in a bad way you can add pieces of angle by rivet or spot weld in unseen areas.
Generally "oil canning" means the metal is popping in and out all the time and may make noise. Wavy is wavy. The terms are intermixed often. Warp is used to describe user caused stretch/shrink......which then is sometimes called oil canning or wavy
P.S. We can't see the "wavy". The patch job looks really good from my house.
