Maybe it's because it's almost dinner time, but I have no idea what you meant by that. How do they know how much people's holdings grow over time and why is this relevant here?
they tracked just addresses' balances I guess. Seems feasible.
It's relevant as a trend of BTC wealth distribution, which seems even more important than a snap at any point in time.
Where are all the addresses whose balance went down? Not in the chart above at least.. I haven't found the methodology yet.