Clojure. Vectors and Lists. cons and peek

Clojure noob here. Playing around with lists and vectors.

> (peek [1 2 3 4])
4
> (peek '(1 2 3 4))
1

Works as promised. Just like this does.

> (cons 1 [2 3 4])
(1 2 3 4)
> (cons 1 '(2 3 4))
(1 2 3 4)

I randomly tried to use peek on the result of cons:

> (peek (cons 1 [2 3 4]))
ClassCastException clojure.lang.Cons cannot be cast to clojure.lang.IPersistentStack  clojure.lang.RT.peek (RT.java:724)

What is going on?