My buddy just bought a house with bitcoin which is wild

Like they literally bought it with bitcoin, or they bought it with the USD or whatever currency proceeds from bitcoin gains? I'd actually be super impressed if it's the former, as it's always seemed more like an investment vehicle (if you're being generous) and not at all a widely applicable medium of exchange.

He sold some of the bitcoin and used it

proceed from BITCOIN cash out - transaction not done in blockchain. Good for him

Apparently it's the currency of choice for black market transactions. Drugs, guns, human trafficking, etc.