We also ran the experiment with the native Linux rsync, i.e syncing Linux to Linux, to rule out issues with Cygwin. Linux rsync performed on average 35% worse than Cygwin rsync, which can be attributed to CPU differences.

Source: https://github.com/google/cdc-file-transfer

I suspect that author made comparison using windows box and linux box with "cpu difference" because those 2 have different spec.