Must be more to it
You just don't send an email saying: wire 5 mil to Shenzen Acme 419 Inc.
There must have been some kind of PO or other dunning for money, which was "authenticated" by the spoofed email saying "yes wire Shenzen Acme 419 Inc the 5 mil."
If the former was the case instead of the latter, I'm not going to buy Ubiquiti products, because a simple spoofed email could order staff to (essentially) embed a stealth rootkit in all their products!