I expect the plane will get hotter than 300 C.
That's my first thought, but presumably they are doing their homework on this. Small objects have the advantage in reentry, since the kinetic energy is carried away ( or left behind ) by a layer of heated ( very thin ) air. For a large object, the size of this layer is comparatively small and the rate of energy loss requires a very high temperature. For a small object, not so much. You would have to do the math, which as I say, I have to believe they are doing.