This is a bit odd, that concurrency would be listed as something they gained from Java, rather than Clojure:

"Clojure: considering the difference between being easy and being simple. Clear difference between data and logic that changes that data. Distinction between pure functions and functions with side effects, try to separate them. Let’s try to make simple code by default."

"Java: performance, concurrency and strictness."

Maybe they mean they were forced to think about concurrency in Java?

I don't think any reasonable person would argue that concurrency is easier in Java than in Clojure.