worth noting that this is the theoretical maximum capacity if the DWDM chassis at all ends were fully populated. Likely using 100, 200 and 400Gbps coherent (QPSK, 8PSK and 16QAM modulated) optics in a 50 GHz ITU DWDM grid. It's not as if it's going to have that capacity at the beginning. And no single circuit will have that capacity.

The math probably looks something like this:

Per 2 fiber pair, 80 channels x 200 Gbps per coherent wavelength = 16000 Gbps

‘roughly the equivalent of simultaneously streaming 5.76 million ultra-high definition videos per second.’

What’s that ‘per second’ doing at the end?

Even removing the "per second" doesn't quite fix it; a data transfer speed can't be "equivalent" to simultaneously streaming N number of UHD videos; it may be equivalent to the speed necessary to simultaneously stream those N UHD videos.

It should be something like, "... will be capable of transmitting data at 144 terabits per second, roughly the speed necessary to simultaneously stream 5.76 million ultra-high definition videos."

Anyway, it was probably just a brain fart.

They assume that an average ultra-high definition video requires 25 megabit per second. Their max theoretical capacity is 144Tbps so the math is: 144Tbps/25Mbits = 5760000 (5.76 million simultanious video streams). Their wording might be confusing but their math is correct.