Like I said, it's best not to think about it too much. The whole thing was a total mess conceptually; I'm sure the original script's version was more plausible before Abrams simplified it.
And yes, black holes' event horizons are spheres or spheroids, but not because they collapsed from stars; after all, the actual singularity of a black hole, which contains all the mass, is a point volume. The event horizon is the surface defining the distance from that point mass at which the escape velocity equals the speed of light -- which is why it's a sphere, since a sphere is a surface whose every point is equidistant from its center. Although it's a bit more complicated if the black hole is rotating, because then the singularity is ring-shaped so the EH is more oblate.
Anyway, screen depictions of black holes have rarely been realistic. Ever since Disney's The Black Hole in 1979, the standard depiction has been a brightly glowing accretion disk that's funnel-shaped in the center like water swirling down a drain, even though a BH wouldn't have an accretion disk unless it had a binary companion to suck gas from (or were a supermassive black hole at the center of a galaxy, surrounded by stars that it tore apart).