Is it rude for a couple to sit in back instesd of split

Hi yall.

So my mom and me had this Argument, my little brother recently started dating a girl and when they got in her car they both went to get in back, she called it rude, i said i wouldnt have cared if they did it when i drove them, their a couple they should be allowed to sit together.

She said its rude, no exception, i said maybe its a generational idea of rude and she said its just rude, i said i dont find it rude, she then insisted i was wrong and anyone else would find it to be rude.

Personally i dont find it rude for a girl to want to sit with her boyfriend instead of awkwardly having one of them in back and one in front, to me it seemed rude to insist someone sit up front with me.

So im curious, what do yall think? Is it rude or na?