This article's word choice using terms like "larping" and "cosplaying" to talk about Mark Twain on a history site seems like a less than ideal writing style; it made me stop reading and facepalm for a moment.
Newfangled?
In this case? Anachronistic still. Anachronistic just means something like "belonging to a different time period," and it doesn't strictly imply earlier or later.
From Oxford Languages:
>a·nach·ro·nism
noun
a thing belonging or appropriate to a period other than that in which it exists, especially a thing that is conspicuously old-fashioned.
"everything was as it would have appeared in centuries past apart from one anachronism, a bright yellow construction crane"
an act of attributing a custom, event, or object to a period to which it does not belong.
"it is anachronism to suppose that the official morality of the age was mere window dressing"