Maybe nothing happened, but he likes whatever he's doing in the morning before they leave. My daughter fights the jacket when I pick her up from daycare. It's not that she doesn;t want to come home, it's that she doesn;t want to leave daycare, because she's usually playing with some beloved toy when I show up to get her. She wants to keep playing, and the jacket means "time to stop playing and leave." I just tell her it's time to go home, and that her puppy is waiting for her at home, and we go. As soon as she's out of sight of the toy she was playing with, she's fine.
It's possible the kid in the letter really likes whatever they do in the morning, and doesn't want to stop playing with whatever it is, or being read to, etc. Or maybe he hates being out in the cold car.
My friend's kid went through this around 2 - 3 years old. He'd cry and whine and refuse to get ready to go when they left the house to go visit anyone. Then, he'd get to whereever they were going, start playing, and not want to leave. He'd throw the same fit he threw about leaving his own house. They'd pretty much ignore the tears, tell him it was time to go and that he could come play again another day, and gather him up to leave. He grew out of it. I think he just got so into whatever he was doing, that he hated to leave while he wa still having fun!