I'd say it's more nuanced. Reading code properly _is_ writing code. Ie i have to work through the logic as if i'm writing it, which is effectively writing it in my head, before i know if that's what i believe to be optimal.

I can _just_ read the code of course, and understand what it does - but just reading isn't analyzing it to the degree you do when you review/write the code. In that level of analysis you're looking for edge cases, bugs, etc. Reasons you'd write it differently. Which i suspect is functionally similar, if not identical, to writing it.