Of course, you are quite right that the year of the armistice was 1918. However, the precise time of the armistice was the eleventh minute of the eleventh hour of the eleventh day, i.e. 11:11 am on Nov. 11. In a host of countries which participated in the war (excluding Germany), "11.11.11' has been enshrined as the most significant marker of the war's end.
Best regards,
Michael