The “thief” in John 10 refers to the false teacher. The day of the Lord coming “as a thief,” in 2 Peter 3, refers to one feature of “thief,” i.e., that he comes unexpectedly.
I agree with what you describe the thief to be in John 10. However Peter is not talking about a thief coming, he is saying that the day of the Lord will come as a thief in the night; I take that to mean that the majority believe the day has already come so they are not waiting or watching for that day.