Any stories you’ve heard about websites enabling CF to survive DDoS were not on the free tier, guaranteed.
Please re-read the description for the free tier. Here’s what “DDoS protection” means on free tier:
Customers are not charged for attack traffic ever, period. There’s no penalty for spikes due to attack traffic, requiring no chargeback by the customer.
Will they use some of their capacity to minimize the DDoS effects for their infrastructure? Sure, I mean they have to whether they like or not, since the DNS points at their servers. But will they keep the website going for Joe Freeloader? Don’t count on that. The terms are carefully worded to avoid promising anything of the sort.