Do you have a citation for this? I've had some stretches in my career where I went a long time without doing any significant coding, and have always been able to ramp back up to speed quickly when needed.
Both my parents used to code (my dad on punchcards and my mom on a massive mainframe). It took significant time for either of them to pick up HTML for side projects.
Even in my own life, I was a developer from 10 to 18 (working 14 to 18, school 10-14) then I took about 7 years off to go do physical sciences. While I retained the basics like for loops and function calls, I totally lost a good portion of the rest of it.
At least in your case, you not only stopped coding but you stopped being around code or dealing with code. That is very different from not coding for 30%. Good chances that if you coded say 5-10% a week and spent the remaining time thinking about code architecture or code reviews, you'd be in a much different position.