I think one must squint a lot to see Julia as a fortress descendant. They seem much more like siblings trying to solve similar problems. Like fortress, Julia does have a reasonable amount of CL/Dylan ancestry with multimethods, etc, but didn’t try any of the fortress style efforts around typeclasses and writing varied code that magically parallelises – you can still get good perf doing typical vectorised stuff like numpy/APL/R, and you get decent perf in loops etc due to the jit and aggressive monomorphisation, and there is fancy stuff for clusters or gpu arrays, but it doesn’t try to achieve the things fortress wanted like making it easy to write code that can be more magically parallelised.
I think in the constellation of languages there's still more intersection of "feature dots" between the two than there is disjunction. Multimethods & numerics emphasis alone makes them uniquely similar, as the latter especially is not a feature that has been mined well in other languages.
Some of the influence is quite conscious, too, from my reading. Though as you mention is obviously a lot of common influence from Dylan and Common Lisp.
And here's a talk by Guy Steele about the Fortress experience, at JuliaCon:
