Hi
Check your settings in the Apple Watch iPhone app under My Watch > Passcode.
Turn Passcode on /off: with this on, Apple Watch can be unlocked by entering either a simple (4-digit) or longer passcode on the watch.
Unlock with iPhone: if enabled, this will automatically unlock Apple Watch at the same time that the paired iPhone is unlocked (using the iPhone passcode or Touch ID). This only happens if you have Wrist Detection enabled and if the watch is on your wrist when the iPhone is unlocked.
If you have both of these settings enabled, your watch will unlock via whichever method you use first (ie put on your watch and enter the passcode or put on your watch and unlock your iPhone).