Gomu Gomu no Ponkan's feed

help im confused i just started reading and currently at chapter 5. the mc transmigrtaed into a game right? a fictional game made by his friend in his ORIGINAL life. so it doesn't make sense for him to be acting like he was regressed into the game? why does he have a grandma? and why does he act as if he's lived his life in the game made. by his friend all along?? did i miss or something? it's just so dumb