It's important to remember that we're talking 1991, rather than present day. While there are a number of older works featuring cryonics, they tend to include themes you probably don't want to expose a ten-year-old to (Heinlein's Door Into Summer) or are soft science fiction or outright fantasy (Star Wars, Captain America), or use a generic stasis instead of cryogenics (Aliens). Harder popular fiction versions like Futurama, Bujold's Mirror Dance, and Cowboy Bebop wouldn't come out for a few years.

There were older hard fiction pieces that mention it -- Niven, at least -- but it's fairly recent for the concept to be an automatic assumption for near-future or even far-future works. If Rationalist!Harry read and remembered everything, he'd have to be aware of it, but honestly he's got a bit too wide of a knowledge base to be reasonable as it is.