When you disabuse someone, you talk them out of a false belief. You do not only say “you are wrong.” You help them see that the thing they were sure of is not true. Though actually, English almost always uses one set shape: disabuse someone of something — of an idea, a notion, a hope. You would not normally say “disabuse someone that…” It is a little formal, a little old-fashioned even, but still alive in careful speech and writing. It is not about “abuse” in the modern sense of hurting someone. You hear it when a person has a sweet but false picture of the world, and someone — kindly or sharply — takes that picture away.