It's an either-or statement. One of the two options, a ship you served on
or another ship you have good relations with. You can't call in a favor from someone you've never met.
Feature: Ship’s Passage
When you need to, you can secure free passage on a sailing ship for yourself and your adventuring companions. You might sail on the ship you served on, or another ship you have good relations with (perhaps one captained by a former crewmate). Because you’re calling in a favor, you can’t be certain of a schedule or route that will meet your every need. Your Dungeon Master will determine how long it takes to get where you need to go. In return for your free passage, you and your companions are expected to assist the crew during the voyage.
It may take months to get home in the scenario I proposed, or at the very least get you closer to home. If it's the latter, surprise surprise the sailor meets yet someone else that owes them a favor.