Even if this were true, these aliens would be ridiculously stupid.

Alien A: "What usable technology and advancements could we hand down to a society of people that has just barely invented writing and is trying to figure out how to use metal?"

Alien B: "How about medicinal plants? Lessons about cleanliness and health? Advanced mathematics?"

Alien A: "No! Give them images of airplanes and flying machines!"

I think it's no small coincidence that the knowledge these aliens supposedly passed on just HAPPENS to coincide with the simplest idiot's concept of the most important advances in human knowledge.