Thanks for the links - Reactive Design Patterns is a great read. On the bottom of the first page, they list FP, futures & promises, CSPs, observers and observables (i.e. Rx), and actors as tools of the trade. Then in the third chapter they look at each tool and evaluate it on the basis of "reactive classification" as per the manifesto (including message passing, which is one of the tenets). In my view, it is not presented as a purely reactive/not reactive dichotomy, but more of a sliding scale - a given tool may satisfy some tenets and not the rest.

Actor model is arguably the most robust with respect to the proposed classification, but the authors also point out that it is not be-all and end-all and that specific problems or even portions of your system may call for different patterns.