Its true and unfortunate. Typescript is the new Coffeescript. It splits the ecosystem. Flow is a progressive enhancement and improves the ecosystem. Typescript has had more push in the mindshare marketing from Microsoft.
TypeScript doesn't split the community any more than Flow does. TypeScript remains very close to ES2016/2017, syntax-wise, with the only major difference being type annotations, but you have those with flow as well. Anybody who can read JavaScript can read TypeScript.