Since you have to convert much of the water in the kernel into water vapor to pop it, that’s not going to happen much below 212 F. That would be a hell of a heat wave. I would say that it is impossible.
I believe there’s a similar story included in Rootabaga Stories by Carl Sandberg.
Carl Sandburg wrote on this topic as well (though the corn was in a barn, not still in the field, IIRC).