He was not surprised because he was already going insane. Since he was hallucinating that the raven was spouting words at him. He was already ill to begin with so it was not a surprise he thought the raven spoke.
Paul Laurence Dunbar was born in 1872, seven years after the proclamation of emancipation proclaimed by Abraham Lincoln in 1863 came into effect. In fact, his parents had been slaves in Kentucky before the secessionist war (1861-1865). Paul Laurence Dunbar became the first African-american poet to gain success and recognition by American society and media. He created a great legacy and became an influence for incoming black poets and artist, and was considered a big figure for other well-known abolitionist figures like Frederick Douglass.