You have been asked to present an epidemiological source for this statement.
Yes, in the beginning the general population was told that only those in direct contact with infected patients care masks. That was when the outbreaks were pretty much confined to those in nursing homes in the Northwest, and people being transferred off of cruise ships. If people started rushing out to purchase masks there would not be enough for those giving direct care. The average person had little to no chance of exposure. That changed as the virus spread.
But AFAIK no one in medicine said that they did not work. The only mask that was rated as worse than nothing were fleece masks, which are face warmers, not real masks. And different materials and styles will make a difference. I had to try various masks until I found the ones that fit me best and were comfortable to wear.
A new study sheds light on what masks work better at preventing the spread of respiratory droplets.
health.clevelandclinic.org
Please note that even the question of whether the fleece mask is worse than nothing has been raised in this article- many media outlets have retracted the original statement as even the Duke researchers did not agree on exactly what conclusion could be drawn.