I have seen this before the last time BITcoin shot up in price everyone wanted a slice of the pie. Sorry for the loss
Trust me I'll do my best to make this not a loss.
People on Reddit were telling me BitPay converts the BTC to cash for the vendors, but that doesn't mean they still have all the BTC(They do)
Of course they might still have
your BTC, but what does that have to do with anything? They received BTC and sent USD. Whether those BTC were yours or not is rather irrelevant. It's also unlikely, since exchanging them would require waiting for two transactions to confirm, and payments via BitPay are instantaneous.
You bought an item listed in USD. Instead of exchanging your BTC for USD and then paying with USD using either an online service or the banking system, you used BitPay to eliminate a few additional, time consuming and potentially expensive steps. Without BitPay, you'd get your refund in USD as well.
Think about it:
You buy an item worth 1,000 USD from a seller while the BTC/USD exchange rate is at 500, so you send 2 BTC to Bitpay and the seller receives 1000 USD. Shortly after paying, the exchange rate climbs to 1,000. If it was up to you, you'd immediately demand a refund, the seller would returns 1,000 USD to Bitpay and Bitpay would return 2 BTC to you.
What prevents somebody from sending 1,000 or 10,000 or even 100,000 USD worth of BTC to either a friend or himself when the course is highly volatile, demand a refund if the exchange rate rises and keep the USD if it falls? It's essentially a sell with a buy-back option. Neither BitPay nor anybody else is going to offer that.