Pair of pants never seen my partner wear

Hi everyone was wondering is it normal to have a pair of pants you own that you never share with your partner my partner normally wear boxers but I found underwear. like white ones in the draw with tag at the back cut out and it been used due to elastic going.
Should I be worried ? Why would a guy have old underwear he doesn’t normally wear? It was hidden in draw of folded clothes. Bare in mind I was only checking to find my underwear because
Somtimes mine end up in his draw.

( they could be my mums as she does live with us only reason I think not is the label is cut out and he cuts his out