How was the ship's crew able to bring the Black on board?

From the text:

Two ropes led from the halter on the horse’s head, and four men were attempting to pull the stallion toward the gangplank. They were going to put him on the ship! Alec saw a dark-skinned man, wearing European dress and a high, white turban, giving directions. In his hand he held a whip. He gave his orders tersely in a language unknown to Alec. Suddenly he walked to the rear of the horse and let the hard whip fall on the Black’s hind quarters. The stallion bolted so fast that he struck one of the natives holding the rope; down the man went and lay still. The Black snorted and plunged; if ever Alec saw hate expressed by a horse, he saw it then. They had him halfway up the plank. Alec wondered where they would put him if they ever did succeed in getting him on the boat.

Then he was on !