If a whale sees 3 NFTs at 0.21 ETH and the next one is at 0.25 ETH, buying those 3 NFTs and listing them for 0.24 ETH is considered manipulation?

No, because if you're doing that, you're not actually tricking anyone else into doing something.

Manipulation is when you mislead or convince others into doing things they wouldn't have ordinarily done. For example, let's say I buy a bunch of avatars from a single collection for super cheap and kept that fact hidden. Then, a few days later, I suddenly start dropping 10 ETH on one or two more of them. The news of those sales would reach Reddit at the speed of light, and others would FOMO in. Once people started FOMOing into the collection, I'd dump my cheaply purchased avatars as the floor price rises. In this case, I have manipulated the market and caused others to buy in at prices they would not have ordinarily considered. Then I used those people to exit at a profit.

Whales commonly do this all the time, and I dare say it happens with 99% of NFT drops. I myself made a large buy early on in this community, and that buy inspired a lot of folks to FOMO in. I didn't dump on them, however. In retrospect, I realized that my big-ticket buy had inadvertently caused others to follow suit. I wasn't intentionally manipulating anyone, and I felt shitty about the externalities my purchase had wrought.

JWPapi has admitted to actual manipulation, and manipulation is shitty. But at least he's being honest about it and seems to want to set things right. I am a believer in second chances, and I am happy to give him one. But I am not buying any Reddit avatars on the secondary market until I see the dust settle here.