They probably raised funds in a private sale or from the more traditional venture capital.
I've never heard of such a coin doing an airdrop and not going through ICO (unless the coin is a scam). I see airdrops as a marketing strategy to introduce the coin/product to potential investors, it's more of an expense really. Potentially, people who benefit from airdrops can also become investors of that coin.
Do you recall how Omisego and Ontology raised funds? Because i just recall them doing airdrops
In the case of Omisego, they raised 25 million dollars from ICO back in 23rd of July, 2017.