From the stated speed and measuring the time it takes to reach an apparent diameter of 1/4 the earth, the red-glowing phase occurs ~2000 miles up. This is inside the exosphere, so some heating is possible from that. There's also a consideration of tidal forces, where the leading edge is being pulled on harder than the trailing one.

I haven't run all the numbers, but it's entirely possible that it would be starting to melt down at that height.