Just because there is no process labelled "Agile" doesn't mean it is meaningless to talk about "doing Agile". What if doing 100% XP by the book turns out to not be ideal or doing 100% Scrum by the book turns out to not be ideal, but the team finds they can achieve good results by mixing and matching their own collection of "agile practices" and even made up practices that are in some way inspired by agile values and principles (yeah I know that sounds a bit wishy washy)? I think in this case it may make sense for the team to claim "we are using a process that doesn't have a name but is inspired by the agile manifesto and consists of a bunch of agile practices that work for us" or for short: "we are doing agile".
As far as I can tell, nobody who has actually taken their process seriously says they are "doing Agile". When you ask them what they do, they give a pretty specific answer. E.g., "Well, we started out with Scrum, but added a number of the XP technical practices and are experimenting with getting rid of iterations for a flow-based approach." Literally every time I have asked follow-up questions of somebody "doing Agile" it has been some variety of horseshit with Agile words thrown in to make it sound trendy.
As an aside, I don't know any serious Agile person who thinks that doing 100% anything by the book is a good idea. I think it was Ron Jeffries, one of XP's inventors, who said something like : "By the book XP is a good place to start, but it probably isn't where you'll end up." Agile processes all have an inspect-and-adapt component. E.g., the weekly retrospectives and continuous tinkering of XP.
