I remember, as a small child, building a powerless radio that vibrated the speaker using the strength of the radio transmission itself. Is ambient backscatter is the same thing, except across much wider frequencies ranges?
Building electronics from scratch is very satisfying. I think I may get into DIY drones soon to scratch that itch.
The device you built uses the incoming signal to power the device as well as drive the speaker. The devices in this article are using the incoming RF signal to both power the device as well as reflect for wireless communication.