the column is a rainfall or a tornado (other way around)?
It's rainfall at high speed. The wind blows downward at 80MPH or more, then when it hits the ground is spreads rapidly in all directions. They're very destructive and being in one feels a lot like a hurricane.
it's a "localized column of sinking air (downdraft) within a thunderstorm" so... both kinda? It's not really rotational, so calling it a reverse tornado is misleading, but its a strong movement of air that can carry water with it... or sometimes it can be dry.
I experienced a lot of those 'dry' microbursts in the Mojave during storms.
Grew up in Blythe, and during the monsoon season (going on right now, actually), had the pleasure of enduring 2 of these microbursts. They are INTENSE.