Update: you seem to be at least partially correct about JS being involved: the webpage source as downloaded from archive.org has a shitton of data in JS structures, while the actual final HTML of that element is nowhere to be found. Meaning the DOM is assembled from the JS data on the fly. Now, the page url, as I predicted, doesn’t seem to figure in this, because the data itself contains numerous instances of ‘web.archive.org’ in it. I’m guessing that Archive’s algorithm replaced the site domain to be prefixed with Archive’s domain and went a bit overboard about it, which seems then to have confused Lemmy’s JS into using the web.archive.org domain as the instance domain when rendering the page.

For better or worse, I don’t use stimulants harder than tea, and amn’t so young anymore as to reverse-engineer this thing further.