As mentioned in this response the button clones and deploys a fresh repo.
However, now with template repositories you can see which template a particular repo was generated from e.g.
Is it possible to update the behavior of the Deploy to Netlify button?
Any specific reason why you need this? The current behaviour has been tested and continues to work, so it would be hard to introduce some changes unless there are significant gains.
it would be nice to credit the original template repo, but it’s mainly the cosmetic change, so no worries if it is too much to implement