Mrs. Obama claimed that the White House was built by slaves and it is well established that slaves made up part of the construction workforce. If all a person knew was what Mrs. Obama said and that it was deemed true by PolitiFact, they might be excused for thinking the structure was built entirely by slaves.

This is why most people think of “truth” as “The whole truth and nothing but the truth”. One could truthfully describe a boy who pushed an old lady out of the way of a bus as a kid who pushes around old ladies. It would not convey the whole truth. Mrs. Obama did not convey the whole truth either — or possibly she is under the misapprehension that the White House was constructed entirely by slaves.