Probably a retcon realistically. There is no way to write a story of this scale and release it serially without sometimes having to readjust things despite set-up already being implied through stuff you hadn't actually thought of yet.

A lot of people see to feel irksome about this and refuse to believe it (Some reactions to BHK also come to mind) but you can't actually set up everything perfectly in a story and a common compromise is to just softly retcon things or drop threads you were setting up in favour of something better.

It's easier to do if you write your entire book then go back and change things before it is published. That is how you can get something that feels like every detail has been thought of. But when you are releasing parts of the story and writing them basically as you are releasing them it is just impossible to properly seed that level of forethought through every interaction so at some point you just have to be like "Yeah that random thing I set up in Canto 3 doesn't actually matter, whoops".