A counterintuitive(?) behavior of dynamic binding demonstrated with Emacs Lisp

add2_dynamic_binding.el

;; Static Binding
(setq lexical-binding t)
t
(defun addx (x)
  (lambda (y) (+ x y)))
addx
(let ((add10 (addx 10))
      (x 3))
  (funcall add10 5)) ;; 10 + 5 = 15
15
;; Dynamic Binding
(setq lexical-binding nil)
nil
(defun addx (x)
  (lambda (y) (+ x y)))
addx
(let ((add10 (addx 10))
      (x 3))
  (funcall add10 5)) ;; 3 + 5 = 8
8
;; The following is the same 
(let ((x 3))
  (funcall (addx 10) 5)) ;; 3 + 5 = 8
8
;; By the way, the following is the normal way to implement such a function in Emacs Lisp
(defun add2 (x y)
  (+ x y))
add2
(let ((x 3)
      (y 4))
  (add2 5 6)) ;; 5 + 6 = 11
11