Can someone else's messages sync to my wife's MacBook?

Found some messages that had synced to my wifes Macbook from her phone. They were not good and when I confronted her she said they were not hers, she had no access to the apple ID or email anymore. Is it possible someone elses messages synced?

All I did was open her messages in November, the last time the phone synced was July. All the messages were from that time frame.

[Re-Titled by Moderator]