If it is an Ada implementation, why wouldn't they call it Ada rather than alang?

In the same way that "the" C/C++ LLVM frontend is called clang and the Fortran frontend is called flang. So a hypothetical Ada frontend could be called alang.

If the language implements the Ada standard (http://www.ada-auth.org/standards/rm12_w_tc1/html/RM-TOC.htm...), it is Ada, regardless of how the particular implementation is licensed.

I wasn't arguing against that, but, yes I agree.