I can't tell if the image is meant as humor - I hope so. The writing isn't over the top, so I didn't catch sarcasm or the absurdity if that was the intention.
Many folks that I know see Cinco de Mayo as an opportunity to be proud of one's heritage and history. For some it is a political expression of a fewer in number beating larger forces.
I've not studied the Battle of Puebla deeply, but found that it was started, if Wikipedia is right, because of a lack of clear and deep communication. Reading that article which included the words - the phrase "wandering about with rifles...thought hostilities had recommenced and felt threatened." The conflict developed. Not too surprising, and pretty much the sort of thing that happens worldwide when the colonizers are running around with guns.
Zooming over time the date/celebration was embraced by the beer companies as a way to sell their wares. Bud and Corona Girls began to dress in a way that reflected connections to Mexican history.
And the TacoMan was begot.