I think he means as in reaching the end of Kabbolas Shabbos.
Similarly (although I can’t think of a city where this happens today), if an entire city or neighborhood brings in Shabbos early, you as a yochid must be makabel shabbos along with them. In every place I know of, there is at least one “early shabbos” minyan and one “late shabbos” minyan, so this would not be an issue. But if you know of someplace that only has “early shabbos”, travelers through that city would need to be careful, or they would be mechallel shabbos.