That makes sense. Let us look at it this way. A spider only spins a web in a location where it can get regular meals. It cannot afford to invest the energy in a web which will not pay off for it.
If a spider spun a web in that location, and made sure to maintain it so vigorously that it knew there was an advantage in reconstructing the web within hours of its destruction, then the area was rife with enough bugs to feed the spider. But if the area was full of bugs, then there is a good chance that many of them made their way into the warm opening of the window and from there into the rest of the basement, where they would naturally be attracted to sources of moisture. And if you have bugs in the basement, then you have a potential source for the marks on JonBenet, which may have been literal bug bites. MEDICOLEGAL INVESTIGATION OF DEATH warns investigators that sometimes flesh wounds which look like abrasions made before death are actually signs of insect feeding made post-mortem.