Why does forward-word stop at this quotation mark?

Question

Minimal example code, run it from emacs -Q. Note the use of unicode RIGHT SINGLE QUOTATION MARK (’) not APOSTROPHE (').

(modify-syntax-entry ?’ "w p" text-mode-syntax-table) ; that's the same syntax as '
(progn
  (switch-to-buffer "test")
  (text-mode)
  (insert "this isn’t a word character?")
  (goto-char (point-min))
  (forward-word 2))

In my Emacs (version 24.5.1) this leaves point on the RIGHT SINGLE QUOTATION MARK in “isn’t”. Why? Shouldn't it move point between “isn’t” and “a” instead?