Here's why:
* "Non-" means "not" or "lacking."
* "Descriptive" means "giving a detailed account of something."
Therefore, "nondiscriptive" would mean "not giving a detailed account." This is a bit awkward and redundant, as the opposite of descriptive is already "non-descriptive."
Possible reasons for using "nondiscriptive"
* Misunderstanding: Someone might have meant "non-descriptive" or "undescriptive."
* Technical jargon: In some specific fields, "nondiscriptive" might be used with a special meaning. It would be important to understand the context to know what it signifies.
If you're unsure about the meaning of "nondiscriptive," it's best to ask the person who used it for clarification.