> All physical objects emit thermal radiation (a.k.a. black-body radiation)

Not all materials are black body emitters. The black body spectrum is in fact an idealized emission spectrum which only few materials approach.

An LED most definitely is not a black body emitter.

You can engineer materials that absorb/emit a specific part of a spectrum and reflect/don't emit in other parts. This has uses in thermal engineering - e.g. you can shed heat by making things "white" in most of the spectrum but "black" in the infrared windows of the atmosphere. In this case they tune the behavior electrically.