I agree with you, that it has to do with perception of reliability. However, the article seems to state that there is an actual greater error with more inputs. That's what I don't understand.

"We cannot remove the error by adding more data inputs and averaging them out, and doing that actually makes the error bigger."

I don't see how it "makes the error bigger". Maybe I'm being too literal and the writer is truly referring to the perception of the results carrying more weight, and therefore having a "bigger error".