DDOS is different from crashing.

And I doubt Facebook implemented something that actually saturates the network, usually a scraper implements a limit on concurrent connections and often also a delay between connections (e.g. max 10 concurrent, 100ms delay).

Chances are the website operator implemented a webserver with terrible RAM efficiency that runs out of RAM and crashes after 10 concurrent requests, or that saturates the CPU from simple requests, or something like that.