The first link is about perception not reality. People consider Millennials to be materialistic. It doesn't say they are.
> Millennials are the most materialistic generation: A new analysis of the European Social Survey shows that across Europe, those aged 21-37 are more likely to agree with a range of materialistic statements. This is especially true in the UK, where 24% say it is important to be rich, compared with 13% of Generation X and 10% of Baby Boomers.
We call this changing the goalposts. It's also logically incorrect as "rich" is a relative measure, not an absolute one.