Eeeh, I still think diving into the weeds of the technical is the wrong way to approach it. Their argument is that training isn’t copyright violation, not that sufficient training dilutes the violation.

Even if trained only on one source, it’s quite unlikely that it would generate copyright infringing output. It would be vastly less intelligible, likely to the point of overtly garbled words and sentences lacking much in the way of grammar.

If what they’re doing is technically an infringement or how it works is entirely aside from a discussion on if it should be infringement or permitted.