We use your 404 custom page title that looks like this here:
It displays pretty often this page correctly when showing a 404. But with some ‘odd’ links it shows a title like this link
The title is taken from the latest post, in this case it is this one: https://www.amaravati.org/dhamma-reflection-from-luang-por-sumedho-just-watching-the-mind/
So when another post is uploaded, it will take that particular title.