Did they give any numbers on the quality of the qubits? For example, IBM's 20 qubit chip has 2-qubit operations with error rates on the order of 5%  (some pairs of qubits are better, some are worse). Quantum supremacy experiments require thousands of operations (tens of layers of parallel operations). Qubits with even a 1% error rate per operation just won't cut it.
1: https://youtu.be/T-8uuq7Izl8?t=26m58s "Experimental quantum computing at IBM" [26:58]
(Disclosure: I work on Google's quantum team.)
I guess taking every branch by default avoids the specter of branch prediction vulnerabilities?
(This is me failing my saving throw vs urge to make terrible nerd jokes.)
What makes one quantum computer superior to another? Not number of qubits, I guess? IBM has a 50-qubit machine.
What is it means for humanity?
I assume these are massive like D-Wave's systems? https://youtu.be/60OkanvToFI?t=392
Is it vulnerable to meltdown?
Breaking Bitcoin With a Quantum Computer
Quantum Resistant Ledger