From Wikipedia:
In computer science, a preprocessor (or precompiler)[1] is a program that processes its input data to produce output that is used as input in another program. […], which is often used by some subsequent programs like compilers.
The emphasis is mine.
Both Typescript and SASS are examples of preprocessors.
By that logic, the C compiler would also be a preprocessor since it converts C code into assembly. Simply calling something a preprocessor just because its output is source code is not logically correct. The same applies to JPlus: the fact that it ultimately produces Java source code does not make it a preprocessor. Internally, it performs compiler-level processes such as AST generation, null-safety checks, and boilerplate code generation, so it should be regarded as a proper compiler.