No, that does not follow.
You're arguing for a sort of technology threshold beyond which we cannot see (presumably within a reasonable time frame). However, which side of said threshold we are on, even for technology from a civilization a million years older, isn't clear. I am not convinced it can be clear, since we'd be arguing about properties of a hypothetical craft.
A time-based argument is probably not useful. The difference between ourselves and ancient Egyptians is huge, but it isn't from exponential change in technology over time. That change in technology was driven by (and drives) both our different (from the Egyptians') model of the world, and our ability to sense the world.
Consider a recovered alien ship hull. If it crashed in ancient Egypt, they might make use of the metals and conclude the ship was a god or its vessel cast down from the heavens. If it crashed in the modern United States, we could figure out the chemical makeup of it, test its properties, hypothesize about how it works, and try to recreate it. All of that could wind up being incredibly valuable, even if we couldn't recreate the shell itself.