In concealing the liar withholds some information without saying anything untrue.
In falsifying an additional step is taken. The liar withholds true information PLUS he presents false information as if it were true.
To pull off the deceit, often, it is necessary to combine concealing and falsifying.
Not everyone consider concealment to be lying. Example a doctor does not tell the patients that the illness is terminal,…, if the husband does not mention that he spent his break with his wife’s best friend, etc.
In these cases the target didn’t ask to be misled and the concealers acted deliberately without giving prior notification of their intent to mislead.
When there is the choice about how to lie the concealing is preferred.
They are both a form of lying.