I have an Xperia Z1 (4.2.2 i think). It is protected with a pattern that i don't know and I am not able to access the recovery mode by holding down or tapping the the volume down key. Some people said tapping should help after the notification light comes on, but the light never shines when turning it on.
No the phone isn't stolen. I work with electronics and people come by to throw their old phones, radios, laptops etc. away and sometimes the devices work and i am allowed to bring them home.