[flashdance]

One public key contains 1.8B USD, but take a look at the address again:

3D2oetdNuZUqQHPJmcMDDHYoqkyNVsFk9r

See how it starts with a 3? Most normal bitcoin addresses start with a 1. The 3 means that it's a pay to script hash address, which means that its likely a multisignature address.

Multisig addresses require multiple signatures to send funds. This could be two out of three possible signatures, seven out of seven possible signatures, fifty out of one hundred possible signatures, it all depends how it is configured.

In short though it kind of works like nuclear weapons where you need multiple keys help by different people to authenticate a transaction.