Nicknames

I recently had a suggested edit declined regarding the Nickname field (using 'Bob' for 'Robert'). They said "Per F*G rules, the nickname is different than the first or middle name."

I don't really care they declined it, but I would like to ensure I am interpreting the site’s guidelines correctly for future suggestions.

The rule states that a nickname is 'different from the real name (first or middle).' Does this imply that the field is reserved strictly for non-derivative names (e.g., 'Spike') rather than common diminutives or shortened versions of the legal first name?