So, I was sitting in the laundromat, browsing my Mastodon feed (hosted at @anthracite 's Dragon.Style. 🙇‍♀️💖) and I tapped a link on my phone from my feed.
It was here at this post where I realized what was going on when I hit OK.

https://dragon.style/@Filene/112723384839682228

So, I got sent to a different URL at the same host domain. Clearly, it's unrelated. But it is revealing. All this accepting of keys that aren't matched, it really needs to be a Red error. Because I had to forget the keys to return to my normal website.

I can imagine so many ways I was attacked. I don't know which. Was I connected to a rogue impostor, or undercover network? Unlikely. Was I hacked at the website to be delivered to the wrong page by a webserver or CDN hack? Also unlikely. I don't think it was my Mastodon or app because Firefox would consistently redirect the link, but not in incognito mode.

So it's more likely the following, if I understand right.
A) if the site is being overwhelmed, I can get hit with a DNS cache poisoning attack among with other users. I think this is called a rebind attack. I doubt this, though the logs might show the server that responded.
B) I could have a root kit on my phone that VPNs my traffic all the time just like the BitVisor Hypervisor. I think I'm still certified on an unrooted phone and a locked bootloader (afaik). But this is no guarantee, and maybe I doubt it. All my traffic??
C) I also doubt this, but what if some of the content returned by the server interrupts and redirects? I doubt this group is copy-pasting Microsoft Doc images into a CMS, so I can't imagine the web server returning this redirect either.

So odd. So personal.