What Synology has done, to make this claim kinda legit, is look at what disks "can" stream (which is more than is listed here) and added the "cap" of the network. So if you do a contrived operation that pushes the drives to their throughput limit (a useless number hence why we don't measure drives by that metric) but tells us nothing about performance. That could be just two or three IOPS producing that limit. But in the real world, that's not useful.