Upvote:9
Have you ever been deported/removed from other countries beside the UK?
Under the circumstances, you should answer yes as your resignation triggered a process required by US Customs and Border Patrol regulations. You had conditional access to US soil in order to go from the ship to your international departure flight.
You can add an explanation that ‘I resigned my job and was allowed to transit from vessel to airport.”
If needed, explain that, under US CPB regulations, a crew member who resigns must have CBP permission to leave the vessel, documents for onward country (passport/visa), and evidence of arrangements (airline tickets etc.). In your case, you were accompanied from the vessel to the airport and, as the only way to do that is landside (i.e., setting foot on US soil), the notation simply says that.
It's very likely that the UKVI understands this sort of action by US authorities, and does not consider it a strike against you. It is better to err on the side of caution and reference it, than to omit and a potential negative impact.