I think you've misinterpreted "modeling a lifestyle". It's not pretense or lack of authenticity. Perhaps "representing a certain type of person" would describe it better.
Portraying yourself enjoying a dignified, secure, middle-class life that you've created for yourself, free from the grind of poverty, and without apology about how far you've come compared to where your ancestors started is a quintessentially American narrative arc that resonates with most of American society, but especially with black Americans.
As far as I can see, the restrained affluence of H&M's home is an element of a visual narrative about who black Americans are and where they belong, that has mirrored the changing fortunes of black people in the US over the last 100+ years.
The look says 'abundance and the expectation of abundance', and it's especially significant as a contrast with the historical experience and portrayal of black people's lives that screamed "not like us" to generations of white audiences - not hard working, not disciplined, incapable of ever improving their lot in life.
The California ranch style furniture and decor and the neutral palette in interior shots of H&M's Montecito home that I've seen are a casually comfortable style, very relatable and accessible to most middle class Americans, including middle class black Americans.
What a representation or modeling of abundance and the expectation of abundance in the home and the California lifestyle of H&M signifies to a black American audience is the overcoming of obstacles deliberately set against it from the earliest days of the colonies. It is an encouraging visual that validates the community's belief in itself and in the possibility of establishing solid, financially secure families and passing on that security to future generations.