If the holder can afford to exercise, and I can assure you that most RH users cannot afford to exercise a single contract(at least on most commonly traded stocks).
Otherwise it's on the broker to sell it at close to someone who can afford to exercise. And who knows if RH pulled that off or not.
I haven't seen official statement, but I did see a couple reddit threads where Robinhood exercised ITM calls without enough funding in the account, then collected the shares and paid the cash difference.
