> strongly suggestive that they have been trained on copyrighted materials
Given that everything -- including this comment -- is copyrighted unless it is (1) old or (2) deliberately put into the public domain, this is almost certainly true.
1 BC should be renamed year 0. Then the years 0-99 are the 0th century, the years 1900-1999 are the 19th century, etc.
To avoid confusion between new style and old style centuries, create a new word, "centan", meaning "100 years" and use cardinal instead of ordinal numbers, for conciseness. Then the years 1900-1999 are the 19-centan.
Imagine Ladybird is developed and is successful. Lots of people use it to read websites.
But then Badcorp takes the code and builds their own varient with extensions. Badcorp is big and has lots of market share. Lots of people use Badcorps's browser, and because lots of people are using it, lots of web developers code for it, including coding for its extensions.
Soon, lots of websites -- including Badcorp's own websites, and they have lots of popular ones -- use the extensions in the Badcorp browser.
Then people still using Ladybird can't use it for most websites. They have lost something.
I note form the demo that there's a "Flat" button that looks like normal text. This is a mis-feature and should be removed; controls should look different from things you can't interact with.