Clojurians Log v2

I don't understand why this delivers two results.

(d/transact conn
            [{:tt 0 :pa "X"}
             {:td 0 :pa "X"}])

(d/q '[:find ?t ?d
       :where
       [?t :tt]
       [?t :pa ?p]
       [?d :td]
       [?d :pa ?p]]
     (d/db conn)) => #{[1 1] [1 2]}

Is this correct?