He came up with it after years of studying steroid users in Boston-area gyms and comparing them not just to non-steroid users in the same gyms, but also to bodybuilders from different eras. For a 1995 study, Pope and his coauthors estimated the FFMIs of Mr. America winners from 1939 to 1959, before steroids were readily available. The group includes future B-movie star Steve Reeves, whose physique was so iconic that he was name-checked in The Rocky Horror Picture Show . The average FFMI was . (One of the highest was George Eiferman, Mr. America 1948, with a FFMI. His upper body was later the model for George of the Jungle, a 1960s cartoon character.) Even today, with all we’ve learned about training and nutrition, an FFMI in the mid 20s is still considered the ceiling for natural bodybuilders. Anything above 26 or 27 is suspect.
There are also many synthetic sex steroids. Synthetic androgens are often referred to as anabolic steroids . Synthetic estrogens and progestins are used in methods of hormonal contraception . Ethinylestradiol is a semi-synthetic estrogen. Specific compounds that have partial agonist activity for steroid receptors , and therefore act in part like natural steroid hormones, are in use in medical conditions that require treatment with steroid in one cell type, but where systemic effects of the particular steroid in the entire organism are only desirable within certain limits. 
I have never seen anything like this happen in any of my TRT patients. And, keep in mind, I have been focused exclusively on TRT since 2012 and have treated thousands of patients during that time. Testosterone injections are very unlikely to cause any significant change with hours of the injection, and if it did, it would likely last for some time as the medication releases slowly and has an 8 day half life. Honestly, I’ve never warned my patients about mixing the two either. I would encourage him to look in to the management of his estrogen levels. Fluctuations there are much more likely to induce behavioral change.