Or maybe he wants the largest possible audience and the comment is aimed at getting him that.

I don't think the criticism was intended in a negative spirit. Getting a native speaker of the language to help edit your writing is a very helpful suggestion. It's a good way to improve your own language skills, while still making your writing available to other audiences. I would definitely encourage people to still publish in their native language though. As you point out, it encourages others to learn other languages and will be very helpful to your fellow countrymen.