I mean, I don't believe the WHO actually stated that in those terms. This is probably a paraphrase of a more nuanced statement that erases the nuance.
https://time.com/6162065/covid-19-airborne-transmission-conf...
>FACT: #COVID19 is NOT airborne.
>The #coronavirus is mainly transmitted through droplets generated when an infected person coughs, sneezes or speaks.
The WHO was unequivocally stating that Covid was not airborne, apparently meaning that they (wrongly) thought it was not spread through aerosols. Instead, they were saying it was spread through droplets. So they were wrong about how it spreads, but did not go as far as saying it wasn't spread through respiratory routes/air at all, which I think might be some people's interpretation of "The WHO said it was not airborne."
"Why the WHO took two years to say COVID is airborne
Early in the pandemic, the World Health Organization stated that SARS-CoV-2 was not transmitted through the air. That mistake and the prolonged process of correcting it sowed confusion and raises questions about what will happen in the next pandemic."