If you have a single server flooding spoofed traffic, it appears as a DDoS to the victim. It's at this point that the distinction between DoS/DDoS breaks down slightly.

It is very much not "trivial" to buy 100Gbps+ of DDoS. I'm highly confident the majority of D/DoS attacks are from single servers, because it works. If you have a 10Gbit server and your target has 1Gbit (or you 1Gbit and them 100Mbit, it still happens), it's not a question of if you can take the target down, but how long you can sustain that traffic level before your upstream notices.

Painting every D/DoS as the most bandwidth ever is a play out of Cloudflare's marketing. If every website operator knew that 1, you don't need that much bigger of a pipe, and 2, you shouldn't buy pipes that charge you $20+/TB like AWS anyway, then Cloudflare would have a much harder time selling you a downgrade in quality, and we would have faster and cheaper networks to boot.