Like the implied advice that folks with 800+ scores have 21+ cards? Ludicrous.
It can go either way. I've seen some posters on here with 20+ w/ scores in the 800s, and I've seen posters with only 2-3 CCs w/ scores in the 800s. One of my favorite posts (not here) was of a poster who only had $1000 in total CLs between 3-4 CCs. Each card was $200-$300. What got her to 800 wasn't the number of CCs (other than not applying like it was a hobby), but it was the 30+ years of reporting that followed those CCs. When you have a bunch of CCs, then odds are that some of them are relatively new and that newer credit hurts (e.g. AAoA). That's why it is not as common to see those with a herd of CCs (20+) have scores in the 800s.