This morning I turned on my phone and when the screen came up it was a screen with the green Android robot and since I didn't have my glasses on the only thing I could read was "Hammerhead" near the top of the screen. My first thought was that it had done a reset but I hit the power button and it finished starting into the normal home screen. This is actually the second time in 2 weeks this has happened.
What is this and should I be concerned?
Edit: This is a Nexus 5 with Kit Kat 4.4.2