Without knowing for sure, I can almost guarantee you this brush was in the outside pocket of someone’s suitcase. Since I started working for a major airline five years ago, I have learned so much about how you should pack your suitcase.
I have seen so many random items on the ramp (the ramp is another name for the tarmac, or the concrete area in the airport). I have seen shoes, makeup, cords, bibs, toothpaste, toothbrushes, pants, and jewelry and that’s just off the top of my head. These items fall out of suitcases because they have been packed in the outside compartment of a suitcase.
If you are checking a bag, there should NEVER be anything of value in those outside pockets. I’m sure the person that belongs to this brush will get to their destination and think that someone has gone into their bag and stolen their brush. When in fact, I am willing to bet that the outside zipper or closure on this bag opened up and this brush fell out of the suitcase. It happens all of the time.