I may be totally wrong ... but maybe not..
In my opinion (only), I believe that Dylan accidentally hitchhiked at the wrong time...
I think that the whole fact that he didn't arrive Saturday night (as per the original plan) threw off the whole visit...I think that his Dad wanted to spend the first night with him - be cause the flight was delayed this was pushed to Sunday. Dylan's friends probably still expected him then..but this would mean that his dad wouldn't have been able to spend the "first" night with him - which, as a dad, would have been important to him..
I think Dylan, being a teenager, believed that he would get up early to catch a drive with his dad to see his friends but, also being a teenager, just needed the extra sleep to catch up..
I think that when he did wake up he was impatient to meet his friends and decided to "get there on his own"...
My son is 17...when his cell phone dies ...he just continues to act - he has never used a landline to explain where he is going or why - he just assumes he will get where he is going...like we all used to do before there were cell phones. When one is young one feels indomitable.
Sadly I think this is a case of "the wrong place at the wrong time>"
I have nothing to back this up...just an inherent belief that the dad is telling the truth. I hope that I am right... Mostly I hope that Dylan is ok- and if not I have a true belief that he is resting with angels..