Well, advocating to hospital staff about the need for interpreters is by definition advocacy
I take your point though. I certainly won't claim to know the exact line that the authors draw on this. My definitions differ somewhat from yours and I'd posit at least some of that is advocacy. Either way, the need to do a better job operationalizing things is pretty much my point.
My default assumption would be that the individuals involved are professional/rationale/reasonable individuals and that advocacy within the context of a professional guideline would be intended as the forms of advocacy that would occur within typical professional contexts (e.g., examples above). Maybe I'm wrong. I literally don't know a single one of the organizers, much to my surprise.