A boy that my daughter baby sits for was confused. He saw our Italian flag in the living room and thought that it was the flag of Mexico. He is Hispanic.
My daughter tried to explain to him the difference. In all fairness they do seem much the same to the untrained eye.
Tri-color flags, or flags with three differently colored stripes, are incredibly popular, and lots of countries have very similar flags. In Mexico's case, the colors represent the banners of the army that liberated it from Spain. In Italy's case, the flag colors represent the official colors of several different Italian kingdoms that joined together to form modern Italy.
So why are they so similar? Coincidence. Flags in the past were primarily for use in battle or to identify naval vessels (often during battle). A simple design with bright primary colors was quick and easy to identify. Given the limited design and limited number of dyes available, replication was bound to happen. Romania and Chad, for example have the exact same flag. Awkward!
Fun fact: the crest on the Mexican flag shows an eagle on a nopal cactus eating a snake, which was the sign of prophecy to the Mexica people were given to indicate their homeland.