Computerworld - https://www.computerworld.com/article/3269566/microsoft-windows/microsoft-unexpectedly-starts-pushing-win10-version-1803-through-windows-update.html#tk.rss_all
As announced, the Windows 10 April 2018 Update, version 1803, became available for download on April 30. If you really want to install version 1803, just go to the download page and click Update now. Fair enough.
What we didn’t expect was an immediate move to push Win10 1803 onto PCs. It now appears that many people, from all over the world, have been upgraded to 1803 — their only transgression being a click on the “Check for updates” button in Windows Update.