Windows 10 does a little trick to speed up boot - when you perform a shutdown, Windows 10 saves a mini-hibernation image to the hibernation file. When you perform normal boot, it can start up quite fast[1]. This gives noticeably shorter boot time especially on spinning rust drives (i know, i know, $CURRENT_YEAR). However if you perform a "reboot" instead of "shutdown + power on", you'll get the full length boot of notably longer time.

[1] assuming the hardware setup is sufficently unchanged