>what we mean is apart from all the visible light from the spectrum, red wavelength is reflected back to our eyes and rest all is absorbed

Actually, no. The perception of red is based on a weighted average of reflectivity at three different wavelengths. https://sciencedemonstrations.fas.harvard.edu/presentations/lands-retinex-theory-experiment#:~:text=What%20It%20Shows See also https://commons.trincoll.edu/wmace/courses/perception/lands-retinex-theory/#:~:text=The%20term%2C%20%E2%80%9Cretinex%E2%80%9D%20was%20coined%20by%20Land%20to,this%20by%20combining%20the%20word%20%E2%80%9Cretina%E2%80%9D%20with%20%E2%80%9Ccortex.%E2%80%9D

So your other question has to be rephrased a bit: what decides at the very root level, which wavelength_S_ to be absorbed _to what extent_ and which _oneS ARE_ is to be reflected _to what extent_. Very few things in the natural world reflect just one wavelength, nor even just one narrow range. For most things in the natural world, there's a mix of reflectances (and there can be other effects, as on butterfly wings).