People show up with their superficially plausible arguments like this one to try and retcon what "open source" means, but there are a few pesky problems.

> Open-source is like a book that can be opened to look inside.

Except every single book that has ever existed also has that property, and you're definitely not calling them "open source". If you did tell someone that a book is "open source" they'd understand you to be saying something else entirely other than that you can look at it.

Sometimes prescriptivism has its merits. The case of "open source" is one of them.