I agree with you though I might have been able to accept them going to "Amish-Tech" -- Even metal plows, wood cutting tools, leather tanning, etc. etc. were all high tech of a certain age or other. But to drop down to sticks and stones is just ridiculous. After working so hard to survive for years, they're now going to ensure that at least 95% of the survivors die in the next two years from simple things, like lack of food, or lack of gear to analyze berries and roots aside from the "what happens when I eat this" test. They should have just pulled a Cavil -- at least they'd have avoided the suffering.
It isn't like their brains went back to stone age. They of course possess all the knowledge of the civilization they are leaving behind. They know how to farm, know how to make weapons, know how to make medicine and drugs, and even understand the theory of computers and could eventually build them if they chose. So they are leaving nothing behind but possessions, not the knowledge that made those possessions.
Anyone can make an omelet with eggs. The trick is to make one with none.