I think it’s similar to this discussion, and see in particular this comment:
Obviously, it was a situation in which someone ported some low-level kernel from Fortran to Julia, discovered some additional optimizations along the way (possibly made easier by Julia), and ended up with a 30% speedup. This kind of thing is not unreasonable — it happens all the time if you have a language in which you can write high-performance code .
Moreover, that thread goes into several examples of ways in which Julia often makes it particularly easy to implement performance optimizations that are awkward (but of course not impossible) in Fortran.