Good point, so in that case it when he was texting with R it may have been while he was still in the truck but possibly not in the house? There is no way these particular text were done while the movie was playing. They had to get into the house with whatever they bought, get the player, set it up, put the movie in etc.
I hear what you're saying, and I agree that the texts may well have been before arriving at the house. I just don't believe that it makes MR a liar. MR said that Dylan was on the couch texting during the movie or playing a game or a video or something. He goes on to say that he assumes he was texting. We know that Dylan had an iPod. An iPod looks exactly like a smartphone. The cell that Dylan had was only a flip phone-not capable of video. I believe that MR really didn't know what Dylan was doing except that he was sitting on the couch messing with an electronic gadget. This is something else that can be establish through forensics. Also, if he were playing a game, he wouldn't necessarily need wifi for that.