I don't agree with you on this. Technology tends to be interdependent on other technologies. Thus i think it would be totally plausible to be able to determine something about the species other then they were better then us at flight. At the most basic level assuming they had flown to earth we would know they had a mastery of space flight and potentially aerodynamics (assuming they landed). This would mean they would have to have mastered certain areas of Physics and thus have an understanding of the areas of mathematics necessary to understand this. In addition most modern engineering problems require large mathematical solutions which would also suggest for advanced space flight they would also need some sort of high speed information processing / simulation capabilities i.e. they developed and discovered some form of computing.

I've only written a short synopsis but there would be a ton of other areas they would likely need to have advanced in as well such as material sciences (to handle vacuum, re-entry, strong acceleration), biological sciences (assuming craft had passengers, if it was artificial or a "drone" then this links back to my point on computer development)