That argument might make sense if the announcement were titled "Expo Sketch: a Playground for React Native". The name they're going with here is clearly "Sketch" not "Expo Sketch"

I see "Native" as a kind of catch-all shorthand for the very large field of mobile apps and architectures.

If Expo had called Sketch, "Expo Designer" then people would indeed call it "Expo Designer". "Designer" is too generic.

"Sketch" isn't though. in mainstream tech parlance, it's associated with one very popular app and company.

One of the "Expo Sketch" devs is in this thread referring to their app as just plain "Sketch".

Time to start a company called Lin that makes a design product called UX

That doesn't make it much better. I thought about white board makers.