Honestly - based on life experience I wouldn't say anything, but I would wonder.
But I'd also keep it to myself, your colleague was rude and unkind.
When I was younger I didn't know the reasons and so took at face value that they just "didn't fancy" having children.
Out of all the people I know who are child free by choice I now know most of them did have unhappy childhoods. And even there in all but one of the cases their sibling/s have had children (that one is an only child). So yeah for 2 siblings to have chosen not to have DC, it would as I say make me wonder.
There's a couple I simply don't know well enough to know what their childhoods were like. And one there's a genetic condition that's behind their decision.
BUT I'm also of a generation where it was fairly unusual still not to have children if you are in a long term relationship. So a fair amount of societal plus family pressure. And I'm aware it's becoming a more acceptable (by society not me) choice so younger women hopefully feel more able to make that choice if it's right for them.
I have a different perspective because I am the unplanned child of a woman who never wanted children (eldest of a big family, wanted a career - which for her generation was seen as mutually exclusive). And who still blames me for changing those plans. So I probably feel more strongly than others that people shouldn't have children unless they genuinely want them.