Interesting read on the probable owner of the site : https://webapps.stackexchange.com/a/149405
If archive.is hosts content that has been removed due to oppressive regimes' policies (including western ones), exposing their identity may put them at risk.
For archive.is, it's lower-stakes, but you might not be able to trust the site as an authoritative source in $x years should (for example) their home government take it over and strategically modify archives for their own purposes.