Pearl: I had the same experience you had, except it concerned the title of my book. I originally called my book Loving Emily, which was an old working title that made sense at the time I coined it, but no longer applied as well after two years of rewrites. The title Loving Emily implied a romance, when in fact the book had morphed into more of a coming of age story about a sixteen year old boy.
So I took a deep breath and changed the title to Any Other Night and changed the cover and book description as well, and I'm really happy I did so. Readers will absolutely complain if a book turns out not to be what they expected. My reviews have been consistently better since I changed the title.
By the way, I also added a warning that my book contained profanity and nonexplicit sexual scenes, which means I no longer get complaints from those readers who turn to YA for squeaky clean entertainment. Again, just a matter of letting readers know up front what they're getting.
I wouldn't freak out over one reader comment. But if you see a pattern over a number of reviews, that's different. Definitely, experiment with your book description, so that you're sure it accurately describes the book. But just know you'll always have a few bad reviews. Everyone gets them.
Good luck!