Ancient scholars in India used the term "Apaurusheya" to indicate knowlege which can not be attributed to the intellect of a specific human being. A poem or a story originates from the intellect of an author. A solution to everyday problems originate from the intellect. On the otherhand, a universally valid principle such as E = mc2 simply reflects through the intellect. It is "apaurusheya" kind of knowledge.
Vedas contain knowledge of the subtle. Rishis were expert meditators. Apaurusheya knowledge reflected in their mindspace. A deeper study of mantras suggests that a big chunk of them are references to universal principles. Expert commentators have emphasized the fact in the past that the references to Vishnu, Shiva Indra and the others in the Vedas are Tattvas or universal principles.
The confusion about Vedas being "apaurusheya" arises from the fact that some mantras contain references to historical (puranas) facts, and some are hints about ritual procedures. Expert commentators in the past could distinguish among these different kinds of mantras. The commentaries of native scholars point to the mantras which refer to universal principles. There appear to be parallels for such mantras in modern science. I have illustrated a few examples in my two books.