It makes no sense to me at all but then very little of what LP says does make sense, IMO. He spouted the same theory last night, saying she drove her car to her parents home after it was seen at Amscot at 7am, but the cell phone pings we have available here don't seem to support it.
Unless Casey has been living on Mars, she probably knows that she can be tracked with her cell phone. If I were planning to dump a body, I certainly wouldn't take my cell phone along. If I were LE, I'd look for times when the cell phone was not in use and the pings didn't move. That's probably when she disposed of the body.