The author starts by noting that the conventional wisdom is that they were separate species because of physical differences. However, the author thinks that because they used similar tools, they were actually one species. The author supports this by saying that this shows clear similarities of behavior despite the fact that they lived in different environments: and that the only way that they would have made such similar tools.
That last sentence will end up being critical. Although we could attack this argument, we don't really need to. The question only asks us what must be false, and here, we only need to use that last point to prove that B cannot be true. The passage told us that the only way the items would be so similar would be if the circumstances and daily challenges they faced were similar. So, it cannot be the case that the daily challenges were different.