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.
https://www.reddit.com/r/wallstreetbets/comments/fcqkmo/so_r...
There's also some threads where it looks like it did not go so well...
https://www.reddit.com/r/wallstreetbets/comments/fd2eko/upda...
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.