why getSimpleName() is twice in com.sun.tools.javac.tree.JCTree$JCClassDecl

I had a weird bug in an application code, which is an annotation processor and I could find that the root cause of the bug was that the class com.sun.tools.javac.tree.JCTree$JCClassDecl contains the method getSimpleName() twice when I query the class using the reflective method getMethods(). The two versions differ only in the return type. This is legal in JVM code, but not legal in Java. This is not method overloading, because it is only the return type that differs and the return type is not part of the method signature.

The issue can be demonstrated with the simple code:

Method[] methods = com.sun.tools.javac.tree.JCTree.JCClassDecl.class.getMethods();
for (int i = 0; i < methods.length; i++) {
    System.out.println(methods[i]);
}

It will print

...
public javax.lang.model.element.Name com.sun.tools.javac.tree.JCTree$JCClassDecl.getSimpleName()
public com.sun.tools.javac.util.Name com.sun.tools.javac.tree.JCTree$JCClassDecl.getSimpleName()
...

(The ellipsis stands for more output lines showing the various other methods that are not interesting for us now.)

The Java version I used to test this is

$ java -version
java version "11" 2018-09-25
Java(TM) SE Runtime Environment 18.9 (build 11+28)
Java HotSpot(TM) 64-Bit Server VM 18.9 (build 11+28, mixed mode)

on a Windows 10 machine.

QUESTION: How was this class code created? My understanding is that this part of the code is written in Java, but in Java this is not possible. Also: what is the aim to have two same-signature versions of a method? Any hint?