Well the name refers to the relative incident and internal angles because that's what scientists first measured. The light slows down due to interactions with the electrons (mostly) in the material. It causes them to move which drags the light. You can model this as an interference from the light produced by the resulting electron movement. I don't see that as bouncing, especially not like the bouncing on the internal surfaces of fiber optics. But obviously it's not like anything we can tangibly understand, so whatever mental model works for you is cool.

In 1999, she led a Harvard University team who, by use of a Bose–Einstein condensate, succeeded in slowing a beam of light to about 17 metres per second, and, in 2001, was able to stop a beam completely.[2] Later work based on these experiments led to the transfer of light to matter, then from matter back into light,[3] a process with important implications for quantum encryption and quantum computing.

https://en.wikipedia.org/wiki/Lene_Hau

It's quantum mechanical, so the maths gets complex. It can be simplified in a useful way however.

Basically, atoms can absorb photons and then re-emit them. You can think of the photon flying past at C, but getting absorbed and emitted along the way, adding delays. In QM however, neat particles don't exist, it deals with quantised, probabilistic waves. The above effect gets blurred over the waveform. No one atom definitely absorbs it or doesn't, it gets blurred together into a general slowing of the wavefront.

I haven't looked into it recently, and the only answer I recall is "because". Ultimately, the higher the refractive index, the slower the speed of light in that substance. As for fiber optics, the 0.66 c, which isn't a claim I made, could be in part due to reflection increasing the path length, or it could be net speed including repeaters/amplifiers, or something else.

The darkness is thicker on earth than in space.