My book gives similar but slightly different explanations of regular grammar and regular language. I doubt it's wrong, is a regular language the same thing of a regular grammar? The definition of my book is: A grammar is regular if all the productions are V-> aW or V->Wa with V,W non terminal or terminal symbols, "a" terminal symbol.W can also be empty or be the same of V.
Regular grammars and regular languages are two different terms:
The same language could be represented with different class of grammars (regular, context free, etc.). A language is said to be regular if it can be represented with a regular grammar. On the othet hand, a regular grammar always defines a regular language. What you have posted is the definition of the regular grammar.
See this Wikipedia post for further information.