I'm not so sure about that. I can read assembly code but I can't write it at a competent level that an employer would require. Reading code is often easier than writing it.

Maybe an analogy is reading vs writing a movie script. A lot of us can read the actors lines and set directions and can then explain what the movie is about -- but most of us are not skillful enough to write a movie script.

The deciphering-vs-generation divide happens in human languages too. Many times, a person learning a foreign language can understand what someone is saying but if asked to generate a sentence to express a thought, they often will be flustered and halting in their speech as the brain struggles to find the next correct word to say.

The reading vs writing skills don't seem to progress equally.