It is stupid because it shows a complete lack of understanding of life experiences different from your own.
There are many reasons people rent instead of buy. In the USA, they could be compromised financially by medical expenses due to serious illness and sold their home to pay the bills, they could be recently divorced and have lost assets to the SO, they could be young and yet to get into the property racket, they could be priced out of the market due to work circumstances, they could have moved recently new a new part of the country and be renting before they buy, they could be waiting for the inevitable property crash in San Deigo to get in cheap, they could ...

There are a million and one obvious reasons why people might rent instead of buy other than not having prioritized buying a home.
Your remark was stupid because you haven't figured this out. My guess is that you are young white, affluent, middle class and live in North America and haven't travelled much.