I know, lots of threads out there and many argue they have more or less issues with distortion. Now, I happened to have had a few lectures - or a few more - in Physics (Optics) back in college and I'm still a passionate photographer.
Here is the basics: All lenses have distortion. The light is redirected, that causes distortion. So what do you do? Easy, you create a lense profile that exactly fits the distortion pattern and corrects the incoming information. That is possible if the lens has a regular distortion pattern, e.g. if the cut of the lense is accurate.
How do you check that? Now, you need a little time, a tripod and a checkerboard pattern. You then put the lens you want to test STRAIGHT in front of the pattern and make sure the orientation EXACTLY fits the one of the checkerboard (linear distortion).
You take a picture.
Now you talk half of the picture (like the right side of your picture), mirror it and see if the mirrored part fits the original (ofc the left part in this case).
This is what I did. Here are the results.
The Sony Xperia XZ Premium distortion issue is a lens issue. The mirrored pattern fits the original pattern exactly, the deviation is zero. Lenses are produced in ridiculously big batches, I doubt that there is even more than one producer. An unclean cut e.g. production waste causes non-linear distortions - but that is not the case here. I'd bet that non of you has distortion different from what I have found, it's about proper testing.
"But I can barely see it on normal pictures" - Yes, because that is how our human brain works. We understand optical patterns as logical and commonly don't see them. What we see is deviations. When tested empirically, 90% of all test participants cannot tell whether or not a picture has common lens distortion (e.g. differs from what you'd see in case u saw it with your own eyes).
So - Sony can handle this by patching an appropriate lense profile.