Perhaps my use of 'objective' in the title was unwise, since everyone taking part in this debate is themselves human (unless there are some seriously fancy chatbots out there). But using again our hypothetical visitors, I don't think they'd be very 'advanced' if they failed to notice the differences in, say, tool use/technology - or any other kind of behaviour, such as social organisation - between humans and other animals. I mean, let's say for the sake of argument that these aliens are as far above us (on some arbitrary 'evolution scale') as we are above slugs; yet it's not hard for human scientists to see that slugs are in turn more advanced than amoebae or bacteria.
I would say that it's not technology per se that makes us different (after all, some human societies have developed next to no technology), but the ability to communicate conceptually. This allows humans to impart specific information to other humans, rather than simply emotions or physical feelings ("Im hungry"/"I'm horny"/"I rank higher (or lower) than you", etc. etc.). The result of this is that every human can access the intelligence and knowlegde contained not just within their own brain, but within a sort of transpersonal 'metabrain' consisting of the accumulated memories, discoveries and inventions of everyone in that society who has lived before, handed down by oral tradition. Of course, this is the most primitive and inefficient way to do this, and it can be vastly increased in scope by the invention of writing, the printing press, electronic communication etc., but it all starts with language.
This is what allows human culture to be accumulative, so that we don't have to reinvent the wheel every time we make a journey, or re-discover fire when we want to cook dinner. As far as I'm aware, this ability to store and transmit information, via verbal and conceptual language, is unique to our species.
I think this uniqueness would be apparent to aliens no matter how advanced they were, even if there were another (perhaps even bigger) 'major objective difference' between us and the aliens.