Yeah, I don't get why people are skeptical. Communist regimes spend billions in internal propaganda, so why wouldn't young chinese men volunteer to defeat the evil imperialists?
Posters were up all over Beijing at the time advertising for volunteers to go to the aid of their Korean cousins. Granted, this is a second-hand story from a man whose uncle was there and told him about it, but that man was upfront about every question I had about the real China. It is my impression that none of them have any reason to make stuff up even though they hold some ideas about the destiny and origin of the Chinese people that differ from mine.