@Lustig Andrei,
The possible manslaughter charge might also relate to his going off course and actually causing the accident, the delay in giving the evacuation order, and his delay in sending out a distress call--all of which would have contributed to the deaths.
I'm not sure there are any laws about a Captain abandoning a ship, the Captain is not obligated to commit suicide and go down with a sinking ship. It mainly seems to be considered a tradition, or an ideal image of bravery and dedication, but it is regarded as a dishonorable act for the Captain to try to save himself while many others are still on-board. This Captain claims he was thrown into the water, either when the ship tilted, or when he tripped over a lifeboat.
But he is expected to remain in charge and organize and assist the passengers and crew in evacuating the vessel. This Captain claims he was supervising the action from his remote location, but the conversation with the Coast Guard officer showed that the Captain really didn't know what was going on aboard the ship, which was why he was ordered back.
We have to wait and see what he will actually be charged with.