What could have caused pocket of fat on the side of my butt? 1 year post op (photos)

To make an accurate assessment regarding the outcome of any plastic surgery procedure we need to see a complete set of proper before and after pictures.
If you don’t have before and after pictures, then ask your surgeon to forward the pictures they took.
It looks to me your provider did liposuction on the upper part of the thigh, probably in order to make your buttocks look bigger.
To me that is not appropriate, unless someone has significant saddlebags.
Your result is a direct reflection of your candidacy for the procedure, and how the procedure was performed.
The result or outcome of those two variables.
To understand your candidacy we need to see before pictures and the results after that is what your surgeon was capable of.
The time to be critical of plastic surgeons is during the vetting process, while having multiple in person, consultations finding the right provider for your needs.
Consider reposting with a complete set of proper before, and after pictures, follow up with your provider or scheduled multiple in person second opinion consultations with other providers in your community.
For second opinion consultations come prepared to bring with you a complete set of before and after pictures and a copy of your operative report.
These are all part of your medical records that you can request from your current provider.
It’s difficult to make a quality assessment based unlimited information
Best,
Mats Hagstrom, MD