Yes, you are right. As the hilarious Non-Philosopher's Guide to Philosophical Terms says:
Realist:
Layman's meaning: Hard-headed.
Philosopher's meaning: Someone who believes in the existence of trees; usually hard-headed, but if you mean "realist about everything", decidedly soft-headed.
And since I'm at it, I can't resist myself a few more off-topic quotes:
Utilitarian:
Layman's meaning: Almost precisely cubical and made of concrete, probably a multi-storey car park.
Philosopher's meaning: One who believes that the morally right action is the one with the best consequences, so far as the distribution of happiness is concerned; a creature generally believed to be endowed with the propensity to ignore their own drowning children in order to push buttons which will cause mild sexual gratification in a warehouse full of rabbits.
Benthamite:
Layman's meaning: Substance from the planet Bentham capable of draining the super powers of Wonder Woman, or Spiderman, or some such person.
Philosopher's meaning: Someone who really would ignore their own drowning child in order to push the rabbit-gratification button.
Supervenience:
Layman's meaning: That's it! ... he's the guy that gets killed by Benthamite.
Philosopher's meaning: A one-way dependence relation between properties or facts of one type and properties or facts of another. .
I'm not sure about it being the opposite of everyday uses of the word, but I think you are more or less correct. But there are further complications. For example, sometimes being a reductionist about something is presented as if it were an alternative to being a realist about that something, but there is no consistency in the application of that criterion. Utilitarians are generally classified as realists about ethics, while subjectivists are generally classified as non-realists about ethics, even though both make ethical claims reducible to psychological claims. My own preference is to taboo "realism" and insist that people be more specific about what they are claiming or denying, but this this position has, alas, not yet been widely adopted by the philosophical mainstream.
As for common language, I think what HM means is that a "realist" is usually someone who denies the existence of things, such as fairies. When people in international relations hold a realist) stance, they aren't saying that they believe in something that their opponents don't (as philosophers would), but that they believe in less, while their opponents hallucinate altruism or believe that treaties are ontologically basic objects.
I think you are wrong to say that utilitarians are generally classified as realists. They are only erratically so classified. When you say "even though both make ethical claims reducible to psychological claims," it sounds like you are defining realism as cognitivism.
Utilitarians are generally classified as realists about ethics, while subjectivists are generally classified as non-realists about ethics, even though both make ethical claims reducible to psychological claims.
That's because utilitarians make normative claims and subjectivists (of the kind you're probably thinking of) don't.
"Realism" in the philosophical sense has to be relative to something - Plato's essences, "collective imagination", society, truth are among the subjects that evoke comments that this person is a realist (considers the "something" to be real), and that one isn't.
A philosophical realist w.r.t. fairies is one who believes Fairies are real, while the non-realist says talk of fairies is due to overactive agency detectors or some such thing. It will tend to seem like the opposite of everyday use of the word "realism" -- at least if the subject is one non-philosophers would ever talk about.
I mention this only because I found it a bit difficult to get, and I think I've now "got" it. Correct me if you think I'm wrong.