I thought this too, but someone in the email thread explicitly mentioned the myricom, and the _response_ to that message was that it was purely internal hardware, not useful for others...so it may just be a coincidence.
It certainly seems believable that this is a third-party processor architecture, but Google has a contract with them to build specific models of that processor that meet their needs (possibly alongside some other proprietary hardware, like a high-speed NIC), and those models aren't sold to the general public. That's pretty common outside x86, right? For instance, is there a way for me to buy a BCM2835 other than by buying a Raspberry Pi?