I interpreted that sentence as meaning it was integrated into the JRuby project as a "home" for the project, similar to being under the management of a particular github org. Not that its implementation was in any way changed or integrated into JRuby.
Concretely, TruffleRuby never shared much in terms of the core language implementation with JRuby (essentially the parser and encoding stuff, never core methods/operators/etc).
