Viewing Wikipedia's list of lies, Tyrion is engaging in a half-truth, with a bit of contextual lying thrown in for good measure.
A half-truth is a deceptive statement that includes some element of truth. The statement might be partly true, the statement may be totally true but only part of the whole truth, or it may utilize some deceptive element, such as improper punctuation, or double meaning, especially if the intent is to deceive, evade, blame or misrepresent the truth.
Contextual lie: One can state part of the truth out of context, knowing that without complete information, it gives a false impression. Likewise, one can actually state accurate facts, yet deceive with them. To say "Yeah, that's right, I ate all the white chocolate, by myself," utilizing a sarcasm that is a form of assertion by ridiculing the fact(s) implying the liar believes it to be preposterous.
He tells three people he suspects of treachery, three different stories.
Then he waits to see which one propagates.
Discover the traitor.
Just to spell it out: Tyrion has now told Cersei's three counselors each a different story about his plans for Myrcella. Depending on what story Cersei ends up hearing, Tyrion will know who Cersei's man is.
With the nod to Beta in espionage circles, this might have been called a canary trap or the Barium meal test. A means of deception where information is given and loyalty tested by watching who reveals what information.
A canary trap is a method for exposing an information leak by giving different versions of a sensitive document to each of several suspects and seeing which version gets leaked.