I have successfully tested few Android apps on my Nokia Lumia 920 running Windows Phone 10 Preview. It's even possible to install Amazon apps store or Google Play store itself using this method.
Microsoft Windows 10 v4.4.4 platform name suggest that this is likely a custom Android 4.4.4 ROM developed specially for Windows Phone 10 by Microsoft. Android 4.4.4 is running as a virtual machine in Windows Phone 10.
Pretty fast and snappy especially for a +3 years old Nokia Lumia 920 with only a dual core CPU and 1GB of RAM.