Not necessarily. Dylan was supposed to arrive on Saturday. So.. speculating here .... Dylan made plans to see his friends Sunday, then his flight was delayed and he didn't arrive until Sunday. Dad said too late to go see his friends, so Dylan makes quick plans to go see them Mon. morning early. Dylan had plenty of time prior to the plane trip and even on the plane to make other plans. Maybe someone made plans to go fishing with him at some point prior to the trip, on Monday. Dylan forgot in his excitement to see his friends and rescheduling his time with them.
So the person shows up early Monday, because most fishermen go fishing early or late in the evening when the fish are biting. Dylan thinks - oh cool - we can go fishing for an hour or so and then he/she will take me to my friends house.
This could have been a crime of opportunity for the person - no way he would have known that Mark wouldn't be there (unless it is a friend of Mark's that Mark might have said something too?).
Now... honestly, I think if Dylan had made plans to go fishing with someone, Mom and/or Corey would know, especially if Dylan made the plans before departing on his trip. 13-year olds talk about things like that generally. Or he would have told his friends when he made the Sunday plans. Yeah, I'll come hang out with you on Sunday and then Monday I'm going fishing with blah, blah in the morning, but maybe I can come over in the afternoon. So... I don't know.
I'm pretty convinced that Dylan was at Dad's house given the articles of clothing and the Ipod. What I'm not convinced of, is what happened after that.......
Salem
She did on Nancy Grace - said it was an older, flip phone and he had it smoking.