I don't know specifically but as a layman I'd imagine the satellite breaking up into smaller and smaller pieces due to the rapid heating and the "wind resistanc

I don't know specifically but as a layman I'd imagine the satellite breaking up into smaller and smaller pieces due to the rapid heating and the "wind resistance"(?) from making contact with the atmosphere at high speeds. I'd also imagine that at some point in this breaking-up-process the pieces are small enough to sublimate from the extreme heat, i.e. "burning up".