It's reasonably clear to me this email was anything but random. Take Google out of the picture and this communication never happens. Both the sender and receiver are taking actions with consideration of one single point -- how does this affect my Google search ranking?

If Google weren't the literal default entryway into the Internet, your argument would be valid. There is precedence in this scenario as well. Back in the 90s, many people said the same thing regarding Microsoft and attaining placement on the Windows desktop for new shipping PCs. This was a key element of the DOJ trial.

The argument that a powerful intermediary has no effect on the conduct of others is simply choosing to ignore certain facts.