If my girlfriend and my friends are coming over to play board games and just chill "at my house" why would there be any need to dress up.
It's not like they are having a New Year's Eve party or any other kind of fancy party,,they are just dressed regularly,,just like anyone of us do when we are at home,,,plus it's not like he just got there,he has been there the whole day.
Look at Kristy she is not wearing her booty shorts,,she got on baggy sweatpants and a t-shirt....it's nothing out of the ordinary,,sometimes we on CC like to overthink things and see things that don't exists.