This is an INCREDIBLY common line of reasoning in our society today. To my mind, though, there are two fundamental issues that have to be addressed before we can take a meaningful stab at answering the heart of this assertion:
1) While it's absolutely true that God used human authors, their languages, vocabulary, and styles in recording the message of scripture for us - it does not logically follow from this that the words of scripture are of solely human origin in a similar way to the existence of of musicians, playing with their own styles, techniques, and backgrounds in a symphony would not be an argument against the existence of a composer.
2) This overlooks the fact that the Bible was not written in a vacuum. It was not something that a monk in the 1200's stumbled upon.
- 2a) The history of archaeology is littered with examples of times when "the skeptics proved the Bible wrong" only to discover on further investigation that their findings actually supported the scriptural record. The Tel Dan Inscription is one such example that will have to suffice. Modern researches believed they were secure in consigning Kind David (the second king of Israel from whom the Christ was to descend) to the dust bin of mythology, only to discover an official inscription on a 9th century B.C. stone where an Aramaen king boasts of defeating the "king of the House of David."
- 2b) We have archaeological evidence from the dead sea scrolls and other manuscripts going back to around 200 B.C. These allow us to say with a high degree of confidence that the text of scripture we have today is incredibly faithful to the source materials. This high textual fidelity calls into question the idea that any of its claims could have survived through the ages if its descriptions of events were wildly off the mark or exaggerated. These aren't stories that happened "once upon a time" after all, they claim to have happened in specific places at specific times to specific people. Given this they are highly falsifiable claims, what I mean by this is that Moses can't get away with telling an Egyptian that he covered the whole land of Egypt with a shroud of darkness for three days last week unless he actually did.
Now, I agree; none of this proves that the Bible is true. Yes, it's clearly old, and yes, it appears to be a faithful record, but just because it's the same record of events today as it was a long time ago doesn't mean that it's the word of God, right? In the spirit of the original question: couldn't the Bible's explanation for these phenomena be wildly flawed even if it's reporting on the events themselves is accurate? Maybe not science fiction, but something more along the lines of historical fiction, maybe?
Up to this point (considering only what we've looked at so far), yes, maybe; but that's not all the Bible has to offer. The context we've just established also servers to form an important ground work from an authority perspective. When we look at the prophecies of the Bible, again and again we see things spelled out in great detail before they happen; often LONG before they happen. King Cyrus for example is mentioned by name and his interactions with the Jews are laid out in the book of Isaiah a couple hundred years before he was even born. Similarly, the prophecy against Tyre at the time of Nebuchadnezzer to scrape the city down to the bare rock is fulfilled in exact detail by Alexander the Great when he scraped the city into the sea to form a causeway out to their fortress island. Finally, David's prophecy in Psalm 22:1-18 (written several hundred years before crucifixion was invented) precisely corresponds to the suffering and death of Jesus 1,000 years later down to the mocking words of the crowd and the method the soldiers would use to gamble over his clothing.
Comparing the prophecies of scripture to any other source that claims to have predicted the future before it happened yields a pretty clear distinction. Somehow the scriptures know time and time again what the future holds; far more often than any human (or even group of humans) could hope to on their own. This really shouldn't surprise bible believing Christians though - God laid out the rule to discern whether or not someone is authentically speaking for Him all the way back in Deuteronomy 18:21-22 after all, "... How shall we know the word which the Lord hath not spoken? When a prophet speaketh in the name of the Lord, if the thing follow not, nor come to pass, that is the thing which the Lord hath not spoken, but the prophet hath spoken it presumptuously: thou shalt not be afraid of him."