Clojure explicitly makes '()' and '[]' different, as well as a few other delimiters. '(1 2 3) is a list like in Lisp tradition, but [1 2 3] is a vector. That is the syntax that the parent is talking about.
Yes, specifically [:whatever] is syntactic sugar for (vector :whatever) and {:what :ever} is syntactic sugar for {array-map :what :ever}. CL has the #() syntactic sugar for the first and the #'acons syntactic sugar for the second. So, in fact, Clojure is no more unLISPy than CL in the most quoted respect.
(Quote from CLtL: Many people have suggested that brackets be used to notate vectors, as [a b c] instead of #(a b c). This notation would be shorter, perhaps more readable, and certainly in accord with cultural conventions in other parts of computer science and mathematics. However, to preserve the usefulness of the user-definable macro-character feature of the function read, it is necessary to leave some characters to the user for this purpose. Experience in MacLisp has shown that users, especially implementors of languages for use in artificial intelligence research, often want to define special kinds of brackets. Therefore Common Lisp avoids using brackets and braces for any syntactic purpose.)
