Where did anyone say that Fuchsia was better than Linux?
The title of this document, "Fuchsia is not Linux", is a play on the "GNU's not Unix" backronym for the GNU project, as well as being a way of pointing out that unlike Android, Fuchsia is an entirely different kernel.
I mean, obviously they would write it because they thought it would be better for certain applications than Linux, or better for trying out new ideas, or the like, but I don't see anything claiming that Fuchsia is better.
In fact, Fuchsia has been done as a pretty low-key project for a while, slowly opening up parts but without much fanfare, just repositories being available, and slowly posting more documentation like the link in the OP. I don't really see very much marketing about it, just low key releases of code and more technical information to give people a taste and show the direction they're trying to go in.