Guessing is very different from knowing. The Bible doesn't claim that no man will guess the day the world will end/ Jebus will return. So let's say Christianity is true. If the world had ended on July 29, that wouldn't mean that the person making the prediction actually had the knowledge that the world was going to end on that day. They didn't know it would end. They thought/ believed/ guessed it would end, which is not really even close to knowing. If I made the claim that I was going to win the lottery tomorrow, and it actually ends up happening, I didn't actually know that it would happen. I just made a really good guess. A very lucky guess. The Bible doesn't say no man will guess right. It says that no man knows.
Man, I love these types of answers. They're all nit-picky and precise.
And yes, you are correct as the difference between "knowledge" and "belief" can be considered to be as simple as a matter of choice. A "belief" is that which you choose to believe where "knowledge" is something you have experienced or seen firsthand. It is, however, very easy for us to convince ourselves that a particular "belief" is "knowledge". In your example, after you won the lottery you would say, "I KNEW that was going to happen!" when really you just believed it and it happened to be right.
But interestingly by that definition we can also "know" something which actually is not correct. Grifters depend on this (I've been binge-watching Leverage
on Netflix. Good show). They manipulate your firsthand experience to give you actual "knowledge", even though what you "know" is wrong.
In the end knowledge and belief can easily be confused for each other and both could be right or wrong, though knowledge likely has a much higher chance of being right. That is probably why so many religious people really, REALLY want to think that their beliefs are actually their knowledge. Because knowledge just "feels" right, more valid than a belief.