For those numbers, it was around 18 real cores with hyper threading enabled. Crypto is a great workload for hyper threads. These systems are currently being built up and aren't yet in production. These are with last year's CPUs.
https://openconnect.netflix.com/en/hardware/ has the currently deployed system specs.
There's a little bit of detail in this press release from Mellanox: http://ir.mellanox.com/releasedetail.cfm?ReleaseID=959350
Have any idea how many cores and what kind of network hardware they use push those impressive figures? I would guess there is some network offload involved, as this comparable to memory bandwidth of a single core of that Xeon if I'm not mistaken.