Do euphemisms come in other varieties? ;)
kinda like 'fudging' data
It's combining two events, somehow, to make up a single statment. In this case, Brinkley is saying "Christmas in Cambodia" is not true, but "Christmas" is true (not in Cambodia though), and "in Cambodia" is true (but not at Christmas). The problem is, there is no record of Kerry being in Cambodia at ANY time during his Swift Boat assignments.
Kerry made up the whole thing. It is a lie. And he used the lie to poilitcal advantage, and to advance his personal ambitions. The lie is an assertion that teh US government (ostensibly under Nixon) was lying to the public -- and he continues to use that angle of atack, based on falsehoods. Today, he says the government lied to get us into Iraq. See a pattern here? These aren't "little harmless" lies. These are cold, calculated, and dangerous lies.
A "mongrel phrase" is one of uncertain origin, so it may be true but no one can say for sure. In Kerry's case, and in his own journal, he contradicts his himself, so we know the origin of all these accounts, they just don't match. "Lie" would be accurate, or at the least "conflicting accounts", but this guy can't bring himself to go there (which is why he was picked by Kerry to write his fictional history).