I think you are both right:
of course every new idea grows in the fertile soil of already existing human knowledge, and thus is heavily influenced by it.
Nevertheless, completely new stuff can grow on this soil, too.

Maybe it doesn't happen all too often (as most new things are a remake or combination of existing things),
but still it does happen.

For example, General Relativity, String Theory, Quantum Mechanics, etc.
have certainly drawn on already existing knowledge,
but I think you can still argue they were a completely new approach, not just a remix of previous ideas.