According to the pixiv page, the artist's name is Tenko. Tenko seems to be a character in something else with 10 pictures, so I tried adding a new tag. Did I add it right?

That was the title of the image. The artist's name (Kuku) is actually under their avatar.

Yeah, I was looking at another pixiv page and just noticed that, and came back to change this one, but you beat me to it. Sorry, rather new to pixiv...

But you're already doing better than Jue, who doesn't add artist tags at all.