Opinions pleasee

Ive been with my bf for over 6 months now. He was recently clearing out his room and was making a collage on a cork board full of memories just for his room and he came accross these cards which congradulated him on passing his driving test. He was with his ex for 4 years and she had sent him one while they were together. He still kept it and put it up on his cork board with the other cards he got. Is it weird that he wouldnt just throw something like that away because hes with me now or am i thinking weirdly? It probally sounds stupid but they were together a long time and it just slipped into my head at one point :/ i dont really know what to think because i just let him keep it...