> But since this is "blockchain", is it more like... they weren't polling for the right confirmation/status/update from the blockchain network API thingie?

That's the exact same mistake I referenced. The consuming website should not be in charge of the atomicity of transactions.

It doesn't matter whether the API was used incorrectly, blockchain was used, or finanglesperunk was the technology. The vagaries of the implementation don't matter. Sending money should be atomic with the request instead of whatever this was. The $3.36 Billion in theft should tell you that.

PS Blockchain is a database. You can choose to enforce SALT instead of ACID, but $3.36 Billion should tell you that people aren't doing something right.

No, it's not blockchain. It's a SQL usage error.