He owned several luxury houses and most certanly never bought 2nd hand clothes even if he wore simple clothes. So it was a carefully crafted image, not what he actually did.
It was obviously a well crafted image, but hardly one invented out of whole cloth. For example non of the three homes he owned[0] would classify as luxury by any reasonable rich person standard. His 'luxury' house in Switzerland was probably not even among 10 most expensive houses in town and was significantly smaller than most billionaires garages. His house in Sweden is in the middle of nowhere, the sort of place where 'no one' wants to live and you can pick up large swaths of land for very little money.
edit: here is a picture of "luxury villa" in Switzerland: https://w.cdn-expressen.se/images/7d/e2/7de2bbfb59044fe6bfc3... Don't get me wrong it's a nice place and something for a reasonably successful doctor or lawyer to aspire to, but hardly screams "one of the 20 richest people in the world".
[0] The vineyard was technically owned the Ikea Foundation and not by him personally, and since the wine they produced there was sold at the restaurants at his stores the whole thing was probably considered a business expense for tax purposes. Because that was how he rolled