Apologies I understand more clearly that it is rewriting/overwriting the blockquote now. But that is the javascript hiding the blockquote, it's not "gone". It's still in the html, still visible to scanners and bots (and those with no javascript and perhaps also screenreaders for the a11y folks). Javascript/CSS hides alllll kinds of stuff on the web alllll the time to make pages look/format a certain way.

They're not entirely right, but they're not wrong either. You're running their javascript to power the embed, and so they gave the response "respecting user's deletion".