Of course, it is also possible that couples quarrel and get dark for a while. When they are not angry, they will be blacklisted and want to contact you. At this time, you didn't delete him. He can send you a message unilaterally, but you can't reply to his message. You will be prompted to add him again when replying.
By the way, I just took a look. There is no such contact in the address book, but after the power failure, this person is in the chat record. You can communicate with this person directly from the chat record. If you delete the chat record, you must add it again.
In order to answer you, I specially blacked out the verification. Didn't this give me the best answer?