> here in germany we often say "technisch affin" which means proficient with technology

As a native German speaker, I indeed fell for this false friend. :-(

I’m a native English speaker and I have only ever heard “affine” as a technical term in mathematics, e.g. an affine transformation of vector spaces. I would have had no idea what it means outside of math.

However, OP’s usage seems logical, so I wouldn’t be upset if it became popular!