The Haganah's own military report after the 1948 War concluded that only some 15% of Arabs had left their homes in response to the Arab leadership's call. The majority had fled the fighting in their area or been driven out by Jewish violence, itself orchestrated by the state. I wouldn't rely too much on Efraim Karsh's writings, they are pretty widely criticised in academic circles. He is a revisionist Zionist and much of what he writes is highly selective. Read Beny Morris on him, Morris dismisses him as a reliable historian.