No, referring users is just one component of Ponzi (or multi-level-marketing) and referring is used many places other than Ponzi. Ponzi is when referral income depends on how much money users they refer invest, but with airdrop, there is no need for investment and investing more real money doesn't give you more rewards.

This is Airdrop to existing users of some service or cryptocurrency, but instead of giving out Bytes based on how much you have something else, this airdrop gives Bytes based on your reputation on Steemit. You just need a 49 000 Bytes attestation fee + around 500 Bytes transaction cost (50 000 Bytes to be safe).

Because Byteball cannot be mined like Bitcoin, they need to distribute their coins and they do it in multiple different ways. https://byteball.org/#dist