I really can't confirm that the data that says only 2% of addresses hold 1 Bitcoin is correct. But even though the data is proven correct, maybe because some Bitcoin holders do store Bitcoin in more than one wallet.
Another thing is that some investors keep their funds into exchanges like Binance and hence it is really impossible to track who holds how many bitcoins.
There are about 28 million non-zero Bitcoin addresses. Do you think 560k people holding 1BTC or more is a small number?
Not at all and actually I believe 2% is a massive number because if I would do a survey online and ask how many bitcoins they hold right now there would be like 1 answer among 100 who would say they have more than 1 bitcoin in a single address.
Note when we make transactions we don't send full amounts and the remaining amount in our wallet is then sent to another address. I mean the balance gets spread among several addresses quite quickly.