What you're talking about is "source-available." I.e. being able to read source code but not having licensing rights to redistribute or make changes.

"Open-source" means that being able to modify and distribute changes is built into the license of the code.

For example, Minecraft Java is source-available in that decompiling Java bytecode is trivial - enough so that tools exist which can easily generate a source code dump. However, actually distributing that source code dump is technically illegal and falls under piracy, so it isn't open source.

Edit: I didn't see your edit, this comment is kind of pointless, oh well