It's just another piece of fallacy that many technical books portray. Any suggestions that refer to 2 (or more) dimensional arrays should be ignored, since multi-dimensional arrays are not supported in Java and heeding such advice will lead to further confusion on top of the already existing confusion. This is what I assume your book is erroneously attempting to communicate.
The real point is that a reference whose type is array, cannot be assigned to another reference of a different type (except for java.lang.Object, java.lang.Cloneable or java.io.Serializable with an explicit cast, but that is irrelevant). By no strange coincidence, a reference of type (for example) int (array of int) is not of the same type as a reference of type int (array of array of int) - the distinction is obvious, is it not?
I sometimes think that this forum goes in cycles of questions, with the same question being asked at certain time intervals. I'll say it one more time: Java does not have support for multi-dimensional arrays (and the argument that the JLS quotes the use of multi-dimensional arrays holds no water). http://qa.jtiger.org/GetQAndA.action?qids=63