The conflicting statements on the clothing he was last seen wearing is concerning.
Initial report states specific clothing. Another report contradicts it, then a later report says the clothing he was last seen wearing is unknown. Did Dad actually see Dylan fully dressed at 7:30 am that morning or are the clothes mentioned in the initial report those that are missing ? Take the Blue Devil's hat for example: he had the hat when he arrived and now we can't find the hat in the house, so Dad says he must have been wearing the hat when he left that morning, or did Dad actually see him wearing the hat at 7:30am that morning.
The conflicting timelines of the morning events is also concerning.
Dad says he left at 7:30 am for a 4 hour shopping trip, then another 5 + hours elapses before the dad contacts LE. Dylan's friend expects his arrival at 6:30 am that same morning, 17 miles away. Dad was aware of this planned meeting because Dad contacted the friend the next afternoon looking for Dylan. If Dylan was fully dressed with his hat and shoes on at 7:30 am that morning (as initially reported by Dad), and he knew he was not going with Dad (Dad went shopping without Dylan), then why didn't Dylan contact his friend to tell him he was not coming (no cell phone / electronic trace after 8PM) ? Why didn't Dad just drop Dylan off at the friend's house that morning while out on the shopping trip ?
Taking this new information into account, one possible scenario is: Dylan left the house sometime after 8:00 PM Sunday night, this could include anytime during the night or the next morning before 11:00 am when Dad discovered Dylan missing. Dylan's destination being the friend's house. Perhaps Dylan and his Dad disagreed on his spending the day at the friend's house. This disagreement sufficiently motivated Dylan to leave the house on his own to go to his friend's house under his own power, (walk and hitchhike...). If Dylan left the house on his own intending to go to his friend's house, then this is not a runaway, it's a disappearance.
