Apologies. I read a news article about him being charged with carfentanil possession and assumed the conviction referred to that. Apparently the carfentanil was found in his apartment and he was later caught with the other synthetic opioid.
I guess it was the next logical step in the "smaller quantities of more powerful stuff are easier to smuggle" race, but I'd expect to see more dealers turning up dead from accidental exposure if it became widespread.