As a scholar of Prābhākara Mīmāṃsā I am well aware of how the normative is often disguised as descriptive. "It is seven o' clock" says the mother, but what she means is rather "Get up! You have to go to school".
Similarly, complex discourses about the nature of philosophy, how it was born, e.g., in Greece or in Plato's Republic, and how it developed in (Latin), German, (French) and English, are only meant to say "We are not going to welcome colleagues working on things we do not care for in our departments". Why so? Because as soon as one tries to reason with the authors of the allegedly descriptive statements (as done here by Ethan Mills and here by Amod Lele), one gets answers such as "the universality of philosophy", "the primacy of logical argumentation", "the importance of debate", "the supremacy of reason over tradition" etc. All of them can be easily found at least in some Indian schools.
I am not saying that they are not found in African, Chinese, Mesoamerican philosophy, I am just saying that no matter how restrictive your definition of philosophy, Navya Nyāya, etc., will fit in. Conversely, Thomas the Aquinas, Augustine, Nietzsche etc. will end up being excluded by such definitions. Thus, the argument is in fact overtly not descriptive.
Does it mean that we should try to make philosophers accept at least Navya Nyāya etc? Or should we rather uncover the normativity of the discourse and call for a broader definition of the enterprise of philosophy?
An insightful discussion of the same issue, with extensive quotes and critical reflections about them can be read in Malcolm Keating's blog, here.
Eric Schwitzgebel offers further interesting reflections on the issue in his blog (be sure to check the comments and his accurate replies to the "ignorance justifying ignorance" argument, as well as the labels for the "not really philosophy" and "low quality" arguments).
UPDATE: "Prof Manners" has an interesting post here explaining that articles trying to say that Confucius is not "philosophical" because philosophy is x, y, z in fact only list "generally desirable and admiration-worthy qualities".
(cross-posted on my personal blog, where you can read also some interesting comments regarding the inclusion (or lack thereof) of Islamic philosophy, and on the Indian Philosophy blog, where you can read some comments regarding the organisation of philosophy institutes.)