What is strange? The bag was removed and he did not know about it. Not at all strange. If the FA does not tell you then you do not know.
Strange to me because I was assuming he had the bag stored under the seat in front of him, and I was picturing the the stewardess leaning in to get the bag out.
Have not flown in years. In reading comments on the thread after I had made my comment, I learned a bit from others. Someone suggested he had the bag under his own seat and the stewardess removed it while in the seat behind him.