Semporna paquebot ??

This item here needs a lot of answers. Even though relatively recent with a faint date of 29JUN78, it should be fairly uncommon from the small town of Semporna. The word paquebot was typed in the same font as the address. So was it all done on board a boat heading for Semporna?
The red chops for Urusan Pos (Official Post) and Ketua Pos (Postmaster) Semporna seem genuine enough. The sequence of events here if known would be most interesting.

Semporna is a small coastal town on the south east which is famous as the gateway to the world renown diving sites around Sipadan Island.