There's no such thing as "actual" BTC holder. All the BTCs in the exchange are fungible. A holder of BTC doesn't know if that BTC was loaned to someone else or

There's no such thing as "actual" BTC holder. All the BTCs in the exchange are fungible. A holder of BTC doesn't know if that BTC was loaned to someone else or not. In a sense, what you suggest is exactly what the exchange did: They calculated the number of "actual" BTCs in the exchange, and split the appropriate number of BCHs evenly among everyone.