As someone who read Ender's Game at the age of 11, and consequently a lot more sci-fi since then, It took Eliezer's "You Only Live Twice" post six years later to properly elevate my knowledge of cryonics to actual conscious awareness. It took an actual proponent of the procedure telling me about it and that people are actually doing it in real life for me to notice it as a useful idea.

And the only thing I needed for convincing was the feasibility of the science, not any moral qualms about the implications of it all. I was (and still am) in the same mind-set concerning life extension and widespread immortality as Harry, and a single afternoon reading about the procedure had me basically convinced.

So no, I don't really think it's incredibly unlikely that Harry hasn't properly heard about cryonics as used in the manor he needs. Of course, I'm but a single data point. How many smart kids have you met that are or aren't knowledgable about existing cryonic procedures?