Falsus in uno, falsus in omnibus (false in one thing, false in all things) is a legal principle. That doesn’t stop cranks from misusing it to cast doubt on science that they don’t like. Overall, it’s just another form of black/white dichotomous thinking.
Science and history deniers love to misapply legal principles to arguments over scientific and historical evidence, for example, falsus in uno, falsus in omnibus (false in one thing, false in all things). It’s a useful principle to apply to witness testimony in a court, but it’s not how evidence is evaluated in science and history.