Photo distortion issue I could use some help with

My wife took this photo recently and I noticed some distortion in it while I was going through the batch in Lightroom. Here is the original:

And here is the detail:

I’ve noticed this distortion in photos I take with my DSLR and I don’t know what causes it. This particular photo was shot at 1/3200 sec, f2, ISO 100 and with a 50mm lens. This particular view is visible like this when I zoom in with Lightroom (the single click zoom when developing or viewing photos).

The person my wife took the photo of is out of focus but I have seen this sort of distortion in a number of photos. Is the image quality setting in my camera? The photos are shot in JPG.

Any ideas or tips?