Why were the french so shocked, prior to their defeat, when they attacked the mexican military?

A stunning victory for the Mexicans, against one of the best armies in the world, the Battle of Puebla cost Zaragoza 83 killed, 131 wounded, and 12 missing. For Lorencez, the failed assaults cost 462 dead, over 300 wounded, and 8 captured. Reporting his victory to President Benito Juárez , the 33-year old Zaragoza stated, "The national arms have been covered with glory.” In France, the defeat was seen as a blown to the nation's prestige and more troops were immediately sent to Mexico. Reinforced, the French were able to conquer most of the country and install Maximilian of Habsburg as emperor.
Despite their eventual defeat, the Mexican victory at Puebla inspired a national day of celebration best known as Cinco de Mayo. In 1867, after French troops left the country, the Mexicans were able to defeat the forces of Emperor Maximilian and fully restore power to the Juárez administration.

Espero que esto ayude!

Ernesto (él) va a ir al comedor después de la sala.