Well, there is the hype and there is the reality. Scala got a fame for being good for concurrency because it is a functional language and because of its actors library. Functional languages are good for concurrency because they focus on immutability, which helps concurrent algorithms. Actors got their reputation because they are the base to Erlang's track record of massively concurrent systems.
So, in a sense, Scala's reputation is due to being a "me too" of successful techniques. Yet, there is something that Scala does bring to the table, which is its ability to support such additions to the language through libraries, which makes it able to adapt and adopt new techniques as they are devised.
Actors are not native to Scala, and yet there are already there different libraries in wide use that all seem to be. Neither is transactional memory, but, again, there are already libraries that look like they are.
They, these libraries, are even available for java, but there they are clunky to use.
So the secret is not so much what it can do, but that it makes it look easy.