When a low quality lab in China is producing something that normally costs such a high amount there are always corners cut, quality issues and people manufacturing it that are not using the same quality control and standards you would even get from a compounding pharmacy.
Author William Llewellyn's talk on how the black market of anabolic steroids evolved over the years explains how things like this are made and what sort of contaminates get into gray/black market injectables (regardless of oil or water based).
Anabolic Steroids: an evolving black market (28mins) https://youtu.be/0LL7bL4F9G4