How do you know QED didn’t teach you a single bit of physics?
If you assimilated the corresponding bits of the Feynman lectures (or any other physics you encountered along the way) at all more easily for having read QED at age 9, then it did teach you some physics, albeit in a sense hard to quantify.
If reading its hand-waving stuff about light taking all possible paths at once increased the probability you’d have assigned to (say) something like the Bohm-Aharonov effect if anyone had thought to ask you how likely you thought it, then it did teach you some physics, even in the “Technical” sense. (Whether more or less than one bit depends on how much that probability increased.)
If having notions like path integrals, phase, and stationary action waved at you unintimidatingly didn’t push your thinking about physics in the direction of clearer understanding, then it seems that you were either (1) already implausibly acquainted with them for even an extraordinarily bright 9-year-old, or (2) implausibly impervious to such things for someone capable of reading and enjoying QED. Of course, something could be implausible to me but still true.