As a male student, did I say something wrong to this female professor? A professor and I spoke recently (I'm a grad student), and she told me about her upcoming sabbatical, and I wished her well and was genuinely excited for her and her travel plans.  But the reaction that I got from her was one of caution and displeasure, with no reciprocation of good vibes.  I mostly said stuff like "that sounds amazing that you're going to Country X for Y number of months!  I hope you enjoy your time there, I love Country X!" 

I'm a male student.  Have I possibly said something condescending or disrespectful to a female professor, by showing my excitement about her travel plans? 

When I analyzed it a bit, I came to the conclusion that I would have had the same reactions if a male professor told me of his sabbatical, travel plans.  So, I don't think that I've said anything sexist.  But I am not 100% sure.
From what you've said, it doesn't sound like a sexism issue specifically, but it might have come off that you regarded her sabbatical as a vacation rather than serious work. You might be worrying about this a bit too much--she's probably already forgotten the exchange.