Being a puppymill rescue, perhaps the cage brings back bad memories...
The last Best Friends "Pup my Ride" that we took part in, we had one little Yorkie females, about 5 y/o and 5 lbs. She was so pretty and loved to be in your arms. When she was handed to me from the Best Friend Volunteer, we had to take down their tag info and put them into our crates and into our car and await our next pup. Well...this female was going NUTS!!! crying, screaming, scratching at the crate, spinning and spinning and spinning inside. I honestly thought she was going to have a heart attack. So I took her out a bunch of times and held her, and during this time she was a angel...But once back into the crate, the stress of being in it came out...I can only imagine her first 5 years trapped in a crate, it must have been horrible
Maybe try an expen for him