non-onionsite gives interstitial "Onionsite Has Disconnected" page

This weekend I was catching up on my webcomics, and I left https://questionablecontent.net/view.php?comic=141 on a Tor Browser tab.

Today I noticed that the tab had switched to a "Problem Loading Onionsite", "Onionsite Has Disconnected", "The most likely cause is that the onionsite is offline. Contact the onionsite administrator.", "Details: 0xF2 — Introduction failed, which means that the descriptor was found but the service is no longer connected to the introduction point. It is likely that the service has changed its descriptor or that it is not running." page from the #19251 (closed) feature.

I did a ^U and searched the page source for 'onion' and the string doesn't turn up.

So... maybe some background javascript process on the page loaded something that tried to load an onion service and that failed and something in Tor Browser caught the failure and popped up the page? But my url bar still lists the .net url.

Am I normal? Am I the only one who has experienced this weird behavior? This is Tor Browser 10.0.16 on linux64.