No, it's not wrong to assume single, childless adults and married adults with young children have nothing in common to discuss - it's simply a fact! That doesn't mean these two groups don't have any overlap. For example, Nikhil's original essay highlights how single, childless adults could offer support to married adults with young children through their experience of living an independent life. But such support goes both ways; married adults with young children can also offer valuable advice to single, childless adults that they may not possess, such as perspectives on parenting and balancing family responsibilities.
It's true, though, that there are other commonalities between the two groups, such as interests, hobbies, values, and experiences. The point of Nikhil's essay wasn't that single and married adults have nothing in common; it was that they don't share the same kind of conversations. These conversations can be incredibly meaningful to married adults with young children, who may desire to discuss topics related to parenting, family life, and raising children. For single, childless adults who don't engage in having children or raising a family, these conversations may be less engaging or even irrelevant for their current lifestyle.
This doesn't mean that single, childless adults and married adults with young children can't be friends. However, without any shared experience related to child-rearing and parenting, it's not wrong to assume there's less in common between them conversationally. UrRong! But if we look at it from an optimistic point of view, maybe it's a good thing that two distinct groups get to discover a whole new type of conversation that neither was aware of before!