The question is not about booting, it's about which OS is running the environment where development happens (writing code, compiling code, testing code, etc).
> Clarification: the operating system where e.g. your IDE runs on
If you're developing on a Linux VM that you connect to via a browser tab opened from your Windows laptop, you're developing on Linux for all intents and purposes.
That is, Windows was not doing enough for you so you switched to Linux for dev tasks.
By the same token, if your IDE is running in WSL, for all intents and purposes you're developing on Linux. A virtual machine, sure, but the virtualized OS is a Linux variant. Because installing the IDE on Windows itself was not doing enough for you.
> Clarification: the operating system where e.g. your IDE runs on
If you're developing on a Linux VM that you connect to via a browser tab opened from your Windows laptop, you're developing on Linux for all intents and purposes.
That is, Windows was not doing enough for you so you switched to Linux for dev tasks.
By the same token, if your IDE is running in WSL, for all intents and purposes you're developing on Linux. A virtual machine, sure, but the virtualized OS is a Linux variant. Because installing the IDE on Windows itself was not doing enough for you.