premise: The Sydney Mardi Gras parade began in 1978 as a march and commemoration of the 1969 Stonewall Riots of New York. It is an annual event promoting awareness of gay, lesbian, bisexual and transgender issues and themes Photograph: Lisa Maree Williams/Getty Images
hypothesis: Lisa Maree Williams was born in 1978.
reason: Her birth date is never mentioned in the text. Just because the parades starting in 1978 doesn't mean the picture is from 1978 so we really don't know when she was born. I suspect it was difficult because the year 1978 is mentioned so it thinks it's incorrect for the previously stated reason.