It's not NFS, it's a block storage mechanism. NFS presents a file-based interface, EBS is a block/device-based interface. The underlying implementation isn't widely publicized, but if you think about how a block device works on a Unix and the AWS bigger-is-faster model for non-PIOPS EBS, you can probably draw some reasonable inferences.
> For example, in at least some embodiments, a representative logical local block data storage device may be made available to an executing program via use of GNBD (“Global Network Block Device”) technology.