He registered a company with a name very similar to an existing, legitimate computer hardware manufacturer. Then targeted companies that already had a relationship and already regularly paid invoices to the company with the similar name.
It mentions the victims were "multinational internet companies". The indictment goes farther, saying:
"Victim-1 was a multinational technology company, specializing in Internet-related services and products, with headquarters in the United States"
and
"Victim-2 was a multinational corporation providing online social media and networking services, with headquarters in the United States"
Edit: It mentions that both victims already regularly paid multi-million dollar invoices to the computer hardware company being impersonated. So, if you're trying to guess who the victims are, they are large enough that they run on their own purchased hardware, in fairly large quantities.