Without knowing context, I can’t specifically read into Parnas intent.

In a general sense, this could be taken to mean that there is frequently such a large gap between theory or possibility and reality that to say “theoretically” about an outcome is likely rather just denying its unlikelihood, whatever reason.

In way, it’s similar to anticipating that any sentence starting with “In an ideal world…” is going to describe an outcome unlikely to transpire because of the obvious differences between that scenario and the ideal one.