Hmm… the two buttons match in terms of font, icon and even the white border, the colours match the current interface alongside and the F-Droid logo. Its not matching in terms of size. It could be the size that is throwing your expectation off. Innumerable sites have differently stylized download buttons that reflect the region/pane that they are placed in. For example what I needed to do in this region is match the other bold and high contrast elements and shapes.
I dithered about a bunch of things in this design, but that region is one that I thought just worked. Maybe I’m wrong. There was another guy on here who suggested a 3D button might be neat and so that started as a response to his request and I actually really liked it when I did it.
Shub, have you read this guys Communication Strategy (F-Droid: Communication strategy)?
EDIT: Vectorised fist holding a phone is a cool idea if we were to focus on the ‘take back your privacy’ aspect in a future header image. Maybe for people who have JS enabled we should do this, solely BECAUSE they have JS enabled, 