Also possible that he has two SKR shirts that are identical. Kind of like his "uniform" so he bought more than one of the same shirt.
Also possible since the bodies were in another part of the house, he just helped himself to food and amenities.
I'm sure he packed for more than a day in his trek from CA, so he had other clothing, I'm pretty sure. I know guys pack light but that would be absurd. Maybe he wore that stuff to the concert, wore other clothing the next day (ride home) and changed back into the concert clothes after the murders.