They don't need any "money" all they do in the lending program is taking a certain amount of Hextra coins and giving you back a certain amount of hextracoins later which is smaller when the price increases that's why they pull it up
They wouldnt need money, if we were on an external. But since its internal, the cashout is from their exchange.
smartcrypto is correct Hextra has premined HXTs and they pay loans with them. No need for bitcoin. They keep the value of HXT artificially high so they don´t have to pay too many HXT to lenders...