Was your response to my question biologically determined or was it a matter of conscious choice?

The correct answer to this is "both" (and it is a false dichotomy). My consciousness is a property of a certain collection of matter which can be most compactly described by reference to the regularities we call "biology". Choosing to answer (or not to answer) is the result of a decision procedure arising out of the matter residing (to a rough approximation) in my braincase.

The difference between me and a coin is that a coin is a largely homogenous lump of metal and does not contain anything like a "choice mechanism", whereas among the regularities we call "biology" we find some patterns that reliably allow organisms (and even machines) to steer the future toward preferred directions, and which we call "choosing" or "deciding".