So: They gave a talk at an OS conference. When people asked, they shipped a tape. The only thing less than that they could have done is not give the talk and not shipped the tapes. Which, had they done so, it is true that UNIX would not have taken off.

Which technically makes your claim true. But if you define marketing that broadly, it also makes your claim completely uninteresting. It boils down to "Things that are developed in house, and never talked about to anyone outside, and never shipped to anyone outside, do not take over the outside world". That's true, but it's trivially uninteresting.

You seem to be much more focused on the technical definition of marketing than on the very real differences between the "marketing" of C and UNIX vs. that of, say, Java.

And back to the original point: The marketing of Go has been much closer to the "marketing" of C than to the slick sales job of Java.