Did it smoke when it crapped out? Does not look like it has much blackening on the ends.

There isn't much blackening, and I have no idea, haven't opened it yet.

Oxidized plastic. Result from combination of light, heat, air and time, pretty usual plastic degradation on most lamps using it... It became matter of plastic quality, if this affect only the surface (decent quality), or if such degradation pass deeply trough the volume (cheap, crappy material)...

And the dust on the surface would be simply collected and oxidized dust extracted from the air passing around the relatively hot lamp.

It's only on the surface.