Yeah, but you don't usually snort in when you're in the hospital. He imitated snorting it in that video where ketamine was mentioned. I'm guessing he's seen it at a party.Its also used to start and maintain the effects of Anesthesia. Both are possible/most likely scenarios of he knows what it is.
I'm not doubting that he's on puberty blockers, but I doubt Piggylou takes him to a real doctor / ER. Too much risk of being reported to CPS. But a gender clinic? Sure, they don't ask any questions there apparently.