25 is maybe what they're referring to her peak commercially (even though 21 in the long run sold more), 3.36M first week, Hello broke the youtube record for fastest to a billion and had nutty sales etc. 30, while still doing crazy numbers, doesn't hold a candle to that in the slightest and is not even in the top 15 globally for the decade under people like the Kid Laroi and SZA (who's album released just 10 months ago) while 21 and 25 are both in the top 3 this century.