If a single transaction spends from multiple inputs at once, those inputs almost certainly share a common owner, because only someone holding every one of those private keys could produce the signatures needed to spend them together.
This was already written in section 10 of Satoshi's whitepaper:
As an additional firewall, a new key pair should be used for each transaction to keep them from being linked to a common owner. Some linking is still unavoidable with multi-input transactions, which necessarily reveal that their inputs were owned by the same owner. The risk is that if the owner of a key is revealed, linking could reveal other transactions that belonged to the same owner.
Their "discovery" surprised no one who did basic research.
The authors are basically frauds:
This was already written in section 10 of Satoshi's whitepaper:
Their "discovery" surprised no one who did basic research.