This just isn't how the verb "to know" and the noun "knowledge" are commonly used and understood. By your understanding, it is impossible to know anything about the future. Yet, I know my wife will come home in a few hours. Very few people would object to such usage and people would stand by me and agree how unexpected it was if she failed to return. That our knowledge is imperfect surprises few people in everyday usage.
There's much that can be said about how so many words turn out, in fact, to be very poorly understood especially if when using common sense as basis for definition---but the point is, the article is talking about learning from a scientific standpoint, so the colloquial sense of "knowledge" is irrelevant.
