Everybody says this, all the time. I would like to propose the controversial theory that actually material things do make people happy, at least within certain constraints.
When I was younger I had shitty cheap material things which made me unhappy. Now I have better stuff which makes me happier.
I used to have a shitty unairconditioned apartment. That made me unhappy. Now I have an apartment whose temperature isn't a problem.
I used to have cheap furniture, which was uncomfortable, and that made me unhappy. Now I have better furniture which is comfortable, I am happier.
I used to have a cheap unreliable car, which broke down and made me unhappy. Now I have a reliable, comfortable car I have no reason to be unhappy.
If you're a baseline-unhappy person (as I suspect the author is) then material goods are unlikely to improve your unhappiness. But I'm a baseline fairly happy person, I don't get unhappy unless there's a specific reason, like discomfort or inconvenience. Sensible acquisition of material goods can remove discomfort and inconvenience, thus making you happy.