Apparently the Autoharp is not really a type of Zither, even though it is a popularly held belief.

I've just forgotten for the moment where I read it, but the person who wrote the article said that an Autoharp is as much a zither as a cow is a horse!! Both animals have four legs and eat grass, but the link is at best, tenuous!

The inventor is also disputed... the instrument invented by Zimmermann was not an autoharp and he didn't produce it, the instrument he did produce had already been invented by Gütter (see here)

We have to accept, I think, that an autoharp is rather specialised... if you know what it is, fine, if not, you've really no way of guessing! TV presenters and their researchers always get it right, don't they?!!