[jerf]

50MB feels like "all the 'ancient' text we have" maybe, as measured by the size of the original content and not counting copies. A quick check at Alice in Wonderland puts it at 163kB in plain text. About 300 of those gets us to 50MB. There's way more than 300 books of similar size from the 19th century. They may not all be digitized and freely available, but you can fill libraries with even existing 19th century texts, let alone what may be lost by now.

Or it may just be someone bloviating and just being wrong... I think even ancient texts could exceed that number, though perhaps not by an order of magnitude.