Apparently it's origins aren't very well known:
http://www.bbc.co.uk/dna/h2g2/A807374
It also appears to have been intended as a curse originally, though I see it as a compliment. I suppose the word
"interesting" has different nuances today; differences and change may very well have been disliked a long time ago, though I think we embrace these ideas far more today.
In the above linked article is mentioned a possibly related quote: 'It's better to be a dog in a peaceful time than be a man in a chaotic period.' ... which is pretty lame advice. The story of humanity has been a constant struggle to be man, sapien(t), in the face of seemingly insurmountable odds and tempts to just give up and be a dog. Though, admittedly, most Chinese probably accept the temptation, and lots of us as well, for that matter. It's just so easy being a dog.