By education, I am an engineer. In the professional of chemical engineering, specifically petrochemical or petroleum engineering, unit operations called “catalytic crackers” exist. These “crack” larger molecules into smaller ones. As an example, octane (nC8) can be crackt into propane (nC4) if desired.
All occupations have their own language, whether cryptolect or just technolect. In mine, these are termed “crackers” (definition 5), with sometimes unfortunate effects.
For persons out of the American Engliphere, a “cracker” (definition 11) is an insulting term for someone who is white, lives in “the South” mostly, and is poor, with a strong implication that their housing is a filthy trailer with a trash-strewn yard. One of my grand fathers surprized me one day by actually saying “white trash”, another term.
Since Appalachia was, and is, absolutely unsuitable for plantations, there were few enslaved black people held by landowners there, so “crackers” are a common demonized group.