The oddness lies in Cassie claiming that she didn't get the calls from the Petito's , her idea was that they must have rung the wrong number.. Then, we find that Gabby and Brian had lived with Cassie and her husband for a year or so, the Petito's would have known the number, so then the cloth has to be cut in half again and one could say, oh well then, in that case, Cassie must have got a new number, ... circles can be run in, but when it's three people who don't answer the phone from one family that is frantic over a missing daughter, then it is suspect.
It is not applying logic to invent extra terrestrial reasons for stuff...