Does adb reboot recovery require unlock? I want to remove the LG G3 overshapening thing as instructed here:

http://forum.xda-developers.com/lg-g3/orig-development/kernel-chupachups-kernel-t2943339

To do so I need to reboot in recovery mode.
I've connected my phone to usb and enabled usb debugging and authorized.
When I issue adb devices I can see my phone.
When then I issue adb reboot recovery the phone reboots, the image of the robot with the open hood and a red triangle appears... nothing else happens. Neither the power button works. All I can do is to remove the battery...
So I'm wondering do I first need to unlock the phone?
What you are seeing is the recovery.  You've successfully booted into it.  It displays that image when it hasn't been told by the main OS what it should do (e.g. something like a system upgrade).

However, it's the the stock recovery that comes with the device, which isn't really useful for much besides doing factory resets.  When someone tells you to "flash the zip in recovery", they're assuming that you've replaced the phone's stock recovery with a custom one such as TWRP or CWM.  Installing one of those does require unlocking.