They're presumably referring to the Harry Frankfurt definition of bullshit: "speech intended to persuade without regard for truth. The liar cares about the truth and attempts to hide it; the bullshitter doesn't care whether what they say is true or false."

The bullshitter does have an objective in mind however. There is some ultimate purpose to his bullshitting. LLMs don't even have that. They just spew words.

Thought of the same book when reading the above.