She want taught an existing form of sign language, she was taught a never explained version of signing, which only the people who worked with her knew, and this was never documented in any scientific way for peer review, and the results weren’t reproducable with other gorilla’s or other researchers.

Best case scenarios, the humans involved anthropomorphized the gorilla, and thought they were communicating on a level much higher than they were actually communicating on, do to this.

Worst case, there were lying knowingly, and this was some sort of scam for money.