A very weird requirement indeed. Should already be part of the ATPL.
And you are trying to activate a class rating. Not a license.
And what about just flying in E,F and G space? No radio required. Not that I think it is a good idea.
My advice: Call Austrocontrol and ask them. They are the authority, not the instructor.
Their website has the contact information. And they have a link to Part FCL. Check subsection H on class ratings requirements.