Clojure update-in questions

(def testds {:e [
                {:c :blah :x 1 :y 2}
                {:c :foo :x 2 :y 5}]
            :e1 [
                {:c :blah :x 1 :z 2}
                {:c :foo :x 5 :z 12}]})

repl=> (swap! testds update-in [:e0] conj {:c :zoom :x 1 :y 1})
{:e0 [{:c :blah, :x 1, :y 2} {:c :foo, :x 2, :y 5} {:c :zoom, :x 1, :y 1}], :e1 [{:c :blah, :x 1, :z 2} {:c :foo, :x 5, :z 12}]}
;; Adding a map to the entity vector works at the repl.

(defn create-entity! [state name]
  "adds entity with given name to state atom"
  (swap! state assoc (gensym name) (vector nil)))

(defn add-component! [state e m]
  "add given component c to entity e in the game state"
  (let [entity e
        component m]
    (swap! state update-in (vector entity) conj component)))

repl=> (create-entity! testds :e4)
{:e0 [{:c :blah, :x 1, :y 2} {:c :foo, :x 2, :y 5}], :e1 [{:c :blah, :x 1, :z 2} {:c :foo, :x 5, :z 12}], :e42 [nil]}
;; OK, that looks correct

repl=> (add-component! testds :e42 {:c :bleck :x 1 :y 2})
{:e0 [{:c :blah, :x 1, :y 2} {:c :foo, :x 2, :y 5}], :e1 [{:c :blah, :x 1, :z 2} {:c :foo, :x 5, :z 12}], :e42 [nil], :e42 ({:c :bleck, :x 1, :y 2})}
;; But when using add-component! it appends a new entity vs adding a map to the entity vector.