Yes, I think it was artistic license. It is such a classic FMV that we shouldn't care about the details.

A pic of Sephiroth in AC is this scene involving walking through fire, so I assume they have that scene in the movie. Do we know if there is more detail in the AC cut of this FMV? That might help. By more detail, I mean, as he's walking away, it will look a little more realistic and maybe he avoids the fire a little better?