This seems to be the recommendation when ceiling fans are used.
examples:
"Rooms where ceiling fans are used should have an upward airflow rotation".
http://www.algomapublichealth.com/disease-and-illness/infectious-diseases/novel-coronavirus/covid-19-advice-religious-services-rites-and-ceremonies/
or ï‚· "When using ceiling or portable fans, use upward airflow rotation":
.https://www.toronto.ca/wp-content/uploads/2020/02/8d59-Fact-Sheet_Novel-Coronavirus.pdf
but no explanation whatsoever as to why...
They must have gotten it from somewhere.
I would suggest, without knowing their reasoning, that ceiling fans on their own aren't great in either direction without knowing more about the air flow patterns that they facilitate.
Upward flow where people tend to accumulate may be better than downward turbulence directed at them (and then heading toward others), but why should the air not be drawn downward as laminarly as feasible and removed or filtered?