Image link leads to different canonical link

Pretty interesting case here :)

But I would say this is a different case that 6.3.1 should not be applied here.

My code removed all those image links leading to url starts-with current page's canonical link, you can check the second/third/etc. images. The links all get removed in my template although they all have links in the source page.

Back to the one you reported, it has link:

https://mynintendonews.com/2018/11/05/abyssal-flame-summon-showcase-now-underway-in-dragalia-lost/dragalia_lost_wallpaper_artwork/

while the current page's canonical link is:

https://mynintendonews.com/2019/01/15/summon-showcase-circus-of-dreams-starts-tonight-in-dragalia-lost/

It's totally different urls, one from 2018/11/05, the other from 2019/01/15.

That's why the link is kept, you can't really tell if it's an attachment url or an article page from the url itself. Don't tell me you can tell it from the url paths :) No, It's not reliable, you don't know whether they customize the permalink or not. It could break things.

Hope my explanation is clear for you.