Maybe adding the network socket makes the isolation within the code a requirement as opposed to a best practice. By this mechanism maintaining isolation is a requirement and not something someone can bypass "just this once" but fix it later.
There's a flood of blog posts (including this one I think) that have conflated the two, probably unintentionally. I'm happy that decoupling their systems worked out well for them. I'm not so happy this is fomenting a new fashion for creating unnecessary network API end points.
That isn't to say that you should always combine your services into one big mega-service. Just that dividing up services should be something you do only when it becomes obviously necessary and for good reasons unrelated to coupling.
Perhaps you're both right.