Boyfriend (22M) got me (22F) different birthstone ring

Hello all,

My boyfriend and I just celebrated our one year! He got me a ring to symbolize commitment and it's great, I wear it everywhere. He said that he'd thought it was beautiful and wanted to get my birthstone. I love it so much. Except I found out that he got me the wrong month's birthstone. He accidentally (?) got me the birthstone of his ex's birth month, actually. They are similar look and color and they start with the same letter, so I'm hoping that it's an honest mistake (I know he loves me and wants nothing to do with her, she's even tried disrupting our relationship but he has remained so clearly loyal to me). I don't want to bring it up, because if it was a mistake, I don't want him to associate this ring on my finger with her. I also don't want to criticize this beautiful gift of commitment he has given me (especially since I've really wanted a ring from him). How do I approach this?