Still Android/AOSP based. HarmonyOS is a dodgy rebranding, that is technically accurate but not practically so. HarmonyOS is both a microkernel that can replace parts of Android, and is also a device ecosystem branding.
It makes zero sense for anyone to rebuild what is open source and flourishing. That said, HarmonyOS should bring improvements to Android and devices in general.
I'm also noticing that Google has been moving more and more functionality into Play store, which is closed source, reducing reliance on open source components in Android ecosystem. The most recent proposal I saw was to even get rid of APKs going forward.