Well that right --even now airdrop still exists, just open an account of Freebitco.in and they have still given sats per hour. At least you have bitcoin for free but I don't think what is the minimum amount before you can withdraw. It could be the contest too or any promotion that given bitcoin, you may accumulate once you will win the contest and I did it in Roobet before, I won some bitcoin by joining their contest and it is totally free that you will get in exchange for your art.