The "10x speedup" is for the compilation step from TS to JS, eg how much faster the new Typescript compiler is, not the runtime performance of the JS output.
Theoretically(!) using TS over JS may indirectly result in slightly better perf though because it nudges you towards not mutating the shape of runtime objects (which may cause the JS engine to re-JIT your code). The extra compilation step might also allow to do some source-level optimizations, like constant folding. But I think TS doesn't do this (other JS minifiers/optimizers do though).
Theoretically(!) using TS over JS may indirectly result in slightly better perf though because it nudges you towards not mutating the shape of runtime objects (which may cause the JS engine to re-JIT your code). The extra compilation step might also allow to do some source-level optimizations, like constant folding. But I think TS doesn't do this (other JS minifiers/optimizers do though).