s/hallucinated/fabricated/, please.

arguably: incorrectly guessed*

in a way, all overconfident guessing is a better match for the result than hallucination or fabrication would be

"confabulation", though, seems perfect:

“Confabulation is distinguished from lying as there is no intent to deceive and the person is unaware the information is false. Although individuals can present blatantly false information, confabulation can also seem to be coherent, internally consistent, and relatively normal.”

https://en.wikipedia.org/wiki/Confabulation

* insofar as “guess” conveys an attempt to be probably in the zone