Nim's underlying, perhaps understated philosophy is that it lets you write code the way you want to write code. If you like snake case, use it. If you want camel case, sure. Write your code base how you want to write it, keep it internally consistent if you want, or don't. Nim doesn't really care.
(That philosophy extends far beyond naming conventions.)
What this avoids is being stuck with antiquated standard libraries that continue to do things contrary to the language's standards for the sake of backward compatibility (arg Python!) and 3rd party libraries where someone chose a different standard because that's their preference (arg Python! JavaScript! Literally every language!). Now you're stuck with screaming linters or random `# noqa` lines stuffed in your code, and that one variable that you're using from a library sticks out like a sore thumb.
Your code is inconsistent because someone else's code was inconsistent - that's simply not a problem in Nim.
Could Nim have forced everyone to snake_case naming structures for everything from the start? Well, sure, but then the people that have never actually written code in Nim would be whining about that convention instead and we'd be in the same place. After having actually used Nim, my opinion, and I would venture to say the opinion of most, is that its identity rules were a good decision for the developers who actually write Nim code.