Really? Why on earth would you care? What if they were to indent their code with 3 spaces? Would that be "insane", too? What if they don't like putting in unnecessary braces around one line "if" statements? Insane?
It's a (very common) stylistic choice. It's hardly insane.
I have literally never seen a large-scale open source project or JS style guide that uses snake_case.
The DOM is camelCase. jQuery is camelCase. Node APIs are camelCase. Why on earth do Zurb think their library is any different?