There is a minimum in the fossil record at that time. There may be other explanations for it, but one very reasonable one is that there just weren't very many skeletons to potentially fossilize.
Certainly. However, I am still highly doubtful that there were only 1280 people alive at that time. I'm not sure that this is what the article is claiming; however, it is written in a way that makes it very easy to come away with that message (as evidenced in this comment section).
What are the chances that every person alive today, for example, will still have living descendants in 400,000 years? If people 400,000 years in the future do a genetic study on themselves to determine how many of their ancestors were alive in the year 2023, what percentage of the 2023 population will they be able to account for? My guess is a fair bit lower than 100%.
