"Preliminary" is a key word, as is "clear". The clear evidence came (to the WHO, at least) about a week later. On the same day as the tweet, they provided further information that doesn't fit in a tweet indicating they expected things to potentially change:
> The timeline states that on that date, a WHO official noted in a press briefing that there "may have been" limited human-to-human transmission of the coronavirus between family members and that there was "a risk of a possible outbreak."
"Preliminary" is a key word, as is "clear". The clear evidence came (to the WHO, at least) about a week later. On the same day as the tweet, they provided further information that doesn't fit in a tweet indicating they expected things to potentially change:
> The timeline states that on that date, a WHO official noted in a press briefing that there "may have been" limited human-to-human transmission of the coronavirus between family members and that there was "a risk of a possible outbreak."
The WHO doesn't have a covert intelligence arm, so they only had what information the Chinese were willing to provide at the time. https://www.politifact.com/factchecks/2020/may/30/brian-fitz...