I think that refers to the Wired article http://www.wired.com/2014/07/cockroachdb/

With the tag being sign of pedigree. "A scalable DB from people who worked at a place with huge scale DBs".

Whether it is very convincing or not is another matter, but I am sure it gets more clicks/attention

Yes, it's called social proof. If you're observant you'll notice that people use it everywhere. Of course, social proof doesn't mean guarantees.

Yeah, I feel a bit uncomfortable about using the brand of a previous employer so prominently to promote a different project

Haven't you noticed the pedigree obsession of some in our field?

I was kind of put off by this as well. Does where they worked in the past have anything to do with how useful the project is now or how talented the people are? What if they're doing it on their own because Google thought the project was useless? What if they were fired from Google, or only worked at Google for a month? How does the founders' past involvement with Google mark this project as any more interesting than any other random "Show HN" project?

It is a pretty strange title. Some might interpret it as they started this project after being fired from Google.

I don't think it matters how you try to promote an open source project. The code will ultimately be the determining factor whether the project can support a following. And everyone has access to the code to make that determination independently.

A requirement of a successful project/product is visibility. Ex-Googlers does not imply much more then "used to work there" but if it drives more attention to them, it's good MarCom.

This was based on an internal Google technology, so the "Ex-Googlers" label is actually quite relevant.

Name-dropping has been common since the first salesman.