Windows 10 by default does a hybrid shutdown which is supposed to make it quicker to start back up.

To fully shutdown you can hold the Shift key down while clicking the shutdown button.

Side note. A Restart will do a full shutdown before starting back up.

More info.

https://www.bleepingcomputer.com/forums/t/625963/details-of-shut-down-vs-restart-please/#entry4079503
https://superuser.com/questions/974553/what-does-shiftshutdown-do-in-windows-10