You sound amazing! What a great life you've made for yourself. I feel really sad for you that you are now questioning how your mum feels about you.
Was it a sibling who told you? Whoever it was, I would definitely need to say something either to them or to your mum. It probably should be to them, so they have to face the consequences of their actions.
Could you have it out with them? Tell them you need to talk because you can't forget what they said and it's causing you a lot of pain. And tell them you think you will need to talk to your mum because this is too difficult to deal with and you need to address it.
And could you say to your mum, x told me you have been saying this. I'm very hurt that you would criticise me to other people and I need you to know I'm really happy in my life and proud of what I've achieved. I need to know you won't undermine me to other people again.
And even if you don't actually say any of that, be clear you ARE proud and happy, and you did absolutely nothing wrong. Your mum is judging you by the standards of her generation and she is the one in the wrong. Parents who can't recognise that their adult children have the right to live their own lives and decide their own values, risk damaging their relationship with their children. She is the one who has fucked up here, not you.
But also, remember the maternal relationship is a very complex one. Most parents are quite capable of being very proud of their adult kids in many ways and a bit critical at the same time. It's absolutely classic in my family that mum has no filter and comes out with random criticism of all of us at times. And it hurts because deep down we all want parental approval. And the only way to get 100% approval is to do exactly what they think we should, which would be very unhealthy.
So in a way, this is part of growing up and becoming a truly separate person from your parents. It's quite painful to know they dont fully agree with your choices. But it's essential to know that it's your life to live, not theirs. And you sound like you are doing a cracking job of it.