He is smiling because he has made it to the Americans without being killed.
I’ve read that the Americans sometimes repatriated these guys to the Soviets, if the Russians were close by. I have a book by a Gebirgsjaeger (mountain troops) sniper who was captured by Americans who were going to hand the group over. He escaped, ditched his uniform and just went home.
Czech countryside in the spring. Saw a flowering tree in the footage. The land would fall under enslavement by Soviet communist totalitarian control for over 40 years.