[basic.lval]/10 says about (non-)modifiable lvalues (http://eel.is/c++draft/basic.lval#def:modifiable):

An lvalue is modifiable unless its type is const-qualified or is a function type.

Nothing about arrays. 2 other places in [basic.lval] which mention arrays are:

[ Note: Except when the prvalue is the operand of a decltype-specifier, a prvalue of class or array type always has a result object.
For a discarded prvalue, a temporary object is materialized; see [expr.prop]. — end note ]

[ Note: A glvalue may have complete or incomplete non-void type. Class and array prvalues can have cv-qualified types; other prvalues always have cv-unqualified types. See [expr.prop]. — end note]

Probably the statement is an artifact from the stone age, when [basic.lval] contained

14If an expression can be used to modify the object to which it refers,
the expression is called modifiable.

Well, one can't assign to (==modify) an array using an lvalue of array type (although nobody knows why), so the statement referring to [basic.lval] made sense at that time.

But currently, the statement "Objects of array types cannot be modified" is complete nonsense in this form; see also #1988 (comment)