Of course its true. They are one of the top ten corporate contributors to the Linux kernel. Why? Just to get drivers for Hyper-V into the mainline kernel. They have realised that enterprises usually have a mix of Windows and Linux so they have stopped fighting and are just working with it. Linux now works fine inside of Hyper-V so I am not surprised that is running in Azure. Expect to see Hadoop, MySQL and whatever else running in Azure as well.