I guess my point is even with that type of survey you can tell what tech level a society is. Radio transmissions would be detectable. Atmospheric scans can be done that would reveal hydrocarbons or other artificial chemicals. Orbit North America at night and you can't help but notice all the lights.
Even a simple orbital survey can reveal if the society is primitive or advanced. The survey detected the presence of intelligent life - why else would they even send Kirk back to talk to the natives unless they knew there were natives to talk to?
It seems Starfleet has a custom of sending landing parties straight to primitive settlements despite the Prime Directive. Errand of Mercy, The Apple and even A Private Little War support this. In A Private Little War somebody had to make initial contact with the natives.