This is the origin apparently.

RRB: “My calculations are irrelevant on this point. They are only valid in speaking of the shock reflection.” Ogle: “How fast did it go?” RRB: “Those numbers are meaningless. I have only a vacuum above the cap. No air, no gravity, no real material strengths in the iron cap. Effectively the cap is just loose, traveling through meaningless space.” Ogle: And how fast is it going?" This last question was more of a shout. Bill liked to have a direct answer to each one of his questions. RRB: “Six times the escape velocity from the earth.”

Hypersonic heating is really weird. We only have data going to about mach 17 (the HTV-2 was the fastest solidly atmospheric vehicle I found) but as we go from subsonic, to supersonic, to hypersonic regimes air becomes pretty much incompressible, and forms a really solid shockwave in front of a fast-moving object. Air is a pretty good thermal insulator, so for very fast, blunt objects they actually heat much slower than you might expect.

Tl;Dr it absolutely vaporized, but it likely lasted longer than you might expect.