I think they have probably negotiated a backroom deal with BitPay. They get fiat from BitPay and BitPay covers
the exchange rate risk. Seems like a good deal for both sides. Free publicity and an additional
payment method for the developer and BitPay probably gets a small percentage and has enough experience in handling
BTC related transactions.
Probably you are better off holding your BTC instead of buying one of these apartments (we all
agree that BTC is probably going to 10k or 20k in the near future).