Lost and Found

This happened a few days back but the story goes back almost 2 months back. About 8 weeks before, I left a text-book in the classroom. I could not find who took it and was searching high and low for it. Silly me, I did not mark the book as mine. I sent a lost&found email to the whole class. No one responded, and I subsisted on a borrowed book during that period. About a week back, one guy sends a mail saying he has someone's copy of that book and since it is unmarked, he will give it away on an FCFS basis. Now the juicy part comes. It seems someone else took his marked book and he was also searching for it. Mistakenly or not, my book went to stay with him. After that course ended, it was returned back to him and hence was left with two copies of the same book and so sent out a lost&found email. He says he didn't remember whether he marked the book or not. I wonder if he knew my book was not his, and still kept it with himself?