As a human, you already have knowledge which is similar to knowing the internal dictionary: you can judge what other kinds of words Wordle is likely to avoid (uncommon words, proper nouns, plurals). So I don't think it is cheating.

Thing is, you can develop a very strong intuition for which words are in that list: they're all common words and mostly "main dictionary entries" (you probably won't find a 4 letter noun or verb with "s" tacked onto the end, probably not "ed" or "es" either)

Certainly using the exact list is a step beyond that; but you can in fact get very accurate at guessing which words might be on it without memorizing the list