Some fair comments on my last answer were added, so I'll try to improve it.
"Are they really egyptian paintings of the exodus?" It's possible, I don't know. It's also possible they are not, I also don't know. Here I can't help.
"Are there good reasons to think they're not?" Yes, there are good reasons to think they are not. This is what we call a possible event of zero probability, like a sudden burst of smallpox somewhere. Ie, the probability they are genuine ancient egyptian paintings is nearly zero, or even zero. As the asker notes "it seems like it should've been a big news story". Well, it hasn't. Why? Were there any good reasons involved?
Why is the probability near zero in this case? Well, ancient Egypt was not a democracy. When the president gets something wrong, everybody writes a book about it. Pharaoh was a god, when the Pharaoh got something wrong, it didn't happen! And let someone dare say it did. Ancient egyptians didn't use to carve many hieroglyphs about their defeats, as any historian can confirm. If ever they did write something about a defeat, they would add much sugar to it.
So, this answers the straight question "Are they really egyptian paintings of the exodus? Are there good reasons to think they're not?"
Yet other issues are raised by the asker: "it should've been a big news story" and he quotes someone saying "debate about the historicity of the Exodus should be reopened as a result"
Why is this such a big thing? Why should such a debate be reopened? Let's suppose for a moment someone just found a Torah scroll in the arabian desert which has been dated by all methods available to Science as from 3200 years ago. This would be big news. Should the debate about the historicity of the Exodus be reopened? First of all, historians would be very amazed by the fact that, besides one or two minor points, it's an exact copy of any other modern Torah scroll, but the chemistry doesn't lie: 3200 years old. And that's it. For historians this 3200 year old Torah scroll is no more a reliable source for confirmation of a historic hypothesis than any modern Torah scroll.
For historians a Torah scroll is a source of hypothesis, but they refuse to rely on it to confirm those hypothesis. Here these jews have this text. Maybe it happened, maybe not. Why should we believe them? Until some irrefutable piece of evidence comes to light, this is just a hypothesis, not a fact.
So these paintings come to light. By what powers are these paintings irrefutable piece of evidence? I saw once a video of president Obama kicking a door open. Maybe some egyptians were just fooling. Maybe that tale about crossing a split sea was a common fairy tale in those days which was written by the hebrews their own way and painted by egyptians their own's. What makes these paintings here more reliable than a Torah scroll?
Does anyone really believes that egyptians monarchs took their time collecting unbiased accounts of events and then ordered painters and carvers to depict the truth as realistic as they could? Or are they egyptian paintings and hieroglyphs just fabulous propaganda?
What's the problem with Torah being a reliable historical source when some ancient obscure propaganda can be such?
For me Torah is a reliable historical source. It's a fact that the jews were in Egypt and left it by crossing a split sea. There's no debate to be reopen. If those paintings are chemically proven to be ancient and egyptian, the better. But they don't prove anything, they're just a good depiction of a known fact. What if those paintings showed people crossing the sea in a baloon? Would it prove that Torah is wrong and jews didn't cross by foot a split sea, or would it rather prove those paintings to be an ancient joke?
If it helps, Moshe was sometime an egyptian monarch, so if some scratches on a wall seemingly ordered by an egyptian monarch are the historical truth, then let's just admit a Torah scroll is also the historical truth.
This here http://www.chabad.org/library/article_cdo/aid/3007/jewish/How-Do-We-Know-that-We-Heard-G-d-at-Sinai.htm also answers much.