What about the language you are using enforces real separation of concerns and encapsulation that Java doesn't have?
Seems to me that those principals are not a quality of a language per se but of design principles that can be applied to any language (maybe some easier than others).
Presumably, Periodic was referring to Rails' emphatically opinionated framework, which (under the right circumstances) can shine a light on at least one approach to SoC that may, in turn, lead to a deeper understanding of the underlying principles.
Seems to me that those principals are not a quality of a language per se but of design principles that can be applied to any language (maybe some easier than others).