Additionally, was this a "photoshop" in the first place?

This post had a pixiv source and a bad_id tag up until yesterday. They were removed without any explanation and the same user added photoshop tag simultaneously.

MyrMindservant said:
This post had a pixiv source and a bad_id tag up until yesterday.

Judging by the post history of this post and the parent, the Pixiv source was copied from the parent post, which is a definite no-no if it doesn't match the source exactly (it was already a bad id when this was uploaded).

I'm not sure if decensoring edits are completely forbidden, but I do think they are highly frowned upon.

Sigh, now it was tagged, flagged and even manually deleted as a nude_filter.

You need to be blind to think that this is a nude filter. Parent post is linked and it's damn clear that no clothes were removed, which is the very definition of nude filters.