It’s not a trained response. The story goes that frogs won’t jump out of a pot of water as long as the heat is raised gradually. There’s no classical conditioning involved at all (and the connection of “classical conditioning is Stalinist” is also quite a leap).

As an aside, I’ve heard that story isn’t actually true, but it makes for a decent metaphor. There are other examples of similar things in nature, like weasels will hunt rabbits by doing a “dance” full of confusing motions all over the place as they gradually inch closer to the rabbit, avoiding the rabbit’s flight of flight response.