Drug levels after death are often much higher than when alive. For example, with testosterone, it is often injected into muscle, where it forms a bolus that slowly releases into the system. As it releases slowly into the system, the liver and kidneys deactivate it and excrete it at a certain rate, this causes the testosterone to maintain a stable level.
After you die, your liver and kidneys stop working and you stop excreting the testosterone out of your body. But the bolus of testosterone in the muscle is continuously leeching into the body and building up to very high levels after death, with no way of being removed. This is why after death the levels can be much higher than what was available when alive.
Basically, you can't draw any conclusions from the results apart from that his blood levels when alive would have been much lower than after death.
In your photo it shows he tested negative to a plethora of other popular anabolic steroids.
You bring up a valid point. I skimmed over some of the literature and didn’t fin anything specific to exogenous testosterone. The study you cite is based primarily on forensic chemicals of interest, ie: narcotics, poisons, etc. this one:
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3413259/#R7Focuses on THC, which I picked because it is primarily stored within the fat deposits in the body, similar to injectable test. While they point out that chemicals with greater lipid solubility tend to redistribute themselves to a greater deagree than chemicals with lower lipid solubility, THC didn’t redistribute itself as much as this would predict.
Looks like the definitive guide is this book:

Which I’ll have to review next time I’m at the local research university