This is so bizarre. And yes, it's rude.
How do you ever find out about someone?
How do you ever know their job/family/feelings on something?
Do you not ask your OH how they're day was because it's 'rude'? Or your kids how school was? Or for feedback at work?
Honestly your mum is wrong and she will have lost out by being this way. I can pick up on these sorts of people very quickly and my heart sinks.
The best is when you get two of them together (presumably you and your mum?)
I was in a queue the other day and the 'conversation' went like this of two older women in front of me.
1 - Hi Sandra
2 - Oh hi Rachel! I'm just doing my weekly shop, the prices here are much better, I think the lamb is on offer, they have...
1 - Yes I'm here to get my grandson a present, he's 5 today look here he is (gets phone out)
2 - My Archie is 4 now. Oh he's such a handsome boy. He starts school in September. Here (shoves phone in her face) Look he's got Michelle's eyes you can see, his dad works at....
1 - Ah here it is, this is Louie. (starts scrolling) this was us at the beach last week haha he loved the sandcastles, he said to me 'nanny can we live in a sandcastle' hahahahaha
2- Louie wouldn't like that, he doesn't like sand
1 - Oh here's another one, oh look at him, he had found a ladybird but oh he was so gentle, he put it right on his hand here you can see
2 - Here it is, I knew it was here somewhere. This was Louie when he was 2 oh my gosh he was tiny hes always been on the smaller side, but then so was my Michelle
1 - Best be off, got to get this lamb
2 - Yes, bye then.
I was stood in bafflement 😂
Did either of them leave them 'conversation' thinking 'wow that was great to see her, how lovely to catch up'