Why are two-month-old posts marked derivative_work and parented to to a post only one month old? On what evidence is this claimed to be the original?

Edit: This twitter post is no longer available, but reverse image searches have suggested it was posted around July 3. Despite being reposted here last, the Asta version (post #6577728) has the earliest verifiable date. It was posted to Pixiv on 2023-06-16 10:54. Asuka (post #6406489) followed it 13 hours later, then Ganyu (post #6455852) half an hour after that.

Arcana55 said:

Why are two-month-old posts marked derivative_work and parented to to a post only one month old? On what evidence is this claimed to be the original?

Edit: This twitter post is no longer available, but reverse image searches have suggested it was posted around July 3. Despite being reposted here last, the Asta version (post #6577728) has the earliest verifiable date. It was posted to Pixiv on 2023-06-16 10:54. Asuka (post #6406489) followed it 13 hours later, then Ganyu (post #6455852) half an hour after that.

Han-0v0 runs an illustration class (https://www.tixian.net/post/453.html). It's the same situation as watermelon knee pose and there are many more examples from the same class:

parent:6345714
parent:5414899
parent:5400574
parent:6476518
parent:5437053
parent:6476527
parent:5438085
parent:6363127

I'm assuming they are based on photos of swimsuit models, but I haven't tracked down the originals.