When Microsoft bought Nokia some years ago, they wanted to provide a great alternative to Android phones. The wanted to push Windows Mobile through it's Lumia phones. (But they failed, you know). But there are still a lot of old Windows Phone 8 smartphones, which aren't getting the Windows 10 update.
Triszka BalÃ¡sz has been able to modify CM 13 (based on Android 6.0) to run on the 2013 Nokia Lumia 525.
He doesn't explain how he reached it, but I guess it was a hard work. When you watch the video, you'll also see, that some things don't work perfect, like the touch responses.
Don't expect, that it will be able to install Android on every old Lumia phone, because it requires a lot of work for every single device to modify all the drivers etc. and unlocking the bootloader is also only possible on older Lumia phones.
Have fun watching this video!