Clarification of a difficulty in al-Dhahabi’s authentication of Ibrahim ibn Sa'd

Al-Dhahabi mentioned in the biography of Ibrahim ibn Sa'd, after he had authenticated him,Then he said: that he was skilled in singing, and we know that Imam Malik held that one who engages in singing is an open sinner?
Do not be surprised; evidence is sometimes hidden from scholars, and its meaning is sometimes hidden from them. Sometimes they do not know the evidence, so they build their ruling on a general principle. And sometimes they know the evidence, but its meaning is hidden from them, so they interpret the hadith in a way other than its intended meaning, and disagreement results from that.