All language is imprecise, that’s why there is skill to writing. We usually balance brevity with precision. Your particular case doesn’t really seem like a big deal unless they decide to be sticklers for the intended meaning over the more lax. Usually people are pretty good about their own ambiguity as long as there’s not a huge cost one way or the other. If she’d written three paragraphs explaining the rules more precisely, someone else would be upset for another reason. (not respecting their time, treating them like an imbecile, wasting precious pixels, etc.)... I think once you try organizing people or events, you tend to give others a bit more leeway.