If he was lending or shorting then the BTC would be "tied up" something you professed to find odd, smoothie. If it's lending then recalling his loans would be the tied up period. Shorting, if he was shorting then he has to buy BTC back which is no different then having sold the BTC outright. However if he was acting as the source of BTC for others to short with, then that's a derivative of loaning so the same "tied up" situation as regular lending.
Okay scenario:
Investors give pirate btc
Pirate promises to pay 7% weekly interest.
Pirate gives "clients" btc for USD (lower prices than now)
Clients short btc by selling it on the market hoping to buy it back cheaper to repay pirate.
But since price hasn't gone down in recent months his "clients" will have to buy the btc back at a higher price assuming they sold short.
Now if the "clients" can't buy back Y x 100k btc because they dont have enough fiat..
It's not the "clients" that are going to get the heat for the non-return of investors' btc, but pirate.
Pirate has two options:
1. Buy btc on the market at higher prices
2. Mine them
Both options don't really fair well for him getting all 500k btc in tact by said deadline (week or two, whatever).
**Note: This whole scenario also doesn't really work well in how pirate is able to "make" 7+% each week. Unless his "clients" were dumb enough to pay +7% premium on each bitcoin when buying from pirate, which is retarded lol.
EDIT: That word
shorting is another word for selling in the context you used it in. And if that is true that he shorted bitcoins lent to him then he is fucked because he only has two options above.