This seems pedantic. As a TypeScript user who is aware of the conversations about build performance, the title is not ambiguous at all. I know exactly they are talking about build time.
It was ambiguous to me. When someone says making a language X-times faster, it's natural to think about runtime performance, not compile times. I know TS runs on JS runtimes, but I assumed, based on the title, they created/modified a JS runtime to natively run TS fast.