Why did just recently said i've played 100 rapid games?!
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I got these today as well and was confused, well since I've played almost the same amount of games as you. I believe it is a new award they've introduced since you (and I) got all of them at the same time (5, 10, 25, and 100). The next milestone should be 500/1000, so you'll get it when you reach that figure.
At the moment of writing (16 march 2021) i've played 600 games of rapid. For some reason chess.com decided i earned the achievement 'rapid 100' today, but i reached 100 games of rapid a far while back in time. I'll try to get some pictures of the number of games i played and the 'prestation'.