How?
The short answer is: I don't know.
However, I can share my subjective view on this topic. I believe that there is not only correlation but causality: the condensation process activates or multiplies the virus.
The virus leaves the human body in form of small water based droplets while people are speaking, breathing, coughing, sneezing.
There is an ongoing discussion on what typically happens after:
1. the virus stays in its droplet which falls to the ground due to gravity within 2m distance, or
2. the droplet evaporates and the virus remains in the air in form of aerosol for a longer time, traveling to longer distances
According to this paper on Modeling evaporation of water droplets carrying virus particles the virus can survive in the air in its droplet and tends to spread airborne, that is, without direct person-to-person contact. Water droplets evaporate quickly in a dry environment, where the air is far from saturated with water vapor, while survive longer in relatively humid, nearly saturated environment where evaporation is slower. Therefore, the paper concludes that the virus tends to spread more in cold and relatively humid environments.
However, in the above paper the virus is assumed to survive only in its droplet and to cease to exist as soon as its surrounding droplet evaporates.
So is that the high relative humidity level which plays a key role here? Until mid summer I believed in this too. But this does not explain some major peaks. What is going on in Izrael? Dry and hot climate. Why Izrael but not the surrounding arabic countries? Why the USA?
Also, right from the beginning there have been some arguments about air conditioning. That it may mix interior air and transfer the virus for long distances, eventually even between different parts of the building. That may be the case, but I would like to add another aspect. There is something in common with the cold and relatively humid air and the air conditioning system: condensation. In air conditioning, it is necessary to release the extra moisture from the warm air as the air is cooled - in order to preserve relative humidity at a 30-60% level. This is performed in the evaporator where the cooling is taking place. The condensed water is then drained outside in a specific tube.
I suppose that the virus can remain in the air even without the droplet, in form of aerosol In an inactive state, so that it could not be attached to human receptors. When condensation takes place, it collects some water as surrounding droplet and becomes active again.
I assume the existence of this inactive state because otherwise there would be mass infections everywhere - which is fortunately not the case.
In this model the air conditioner plays a virus activating role - apart from transfering the virus all over in the building. However - as the paper discussed above suggests - in the dry air of the room the droplet quickly evaporates and the virus gets back to its inactive state. Therefore it may play a role how far someone is from the air conditioner. Possibly the 2m rule can be considered here as well?
I believe in this hypothesis because it gives an explanation for the mass virus spread in a lot of cases. I listed some examples on the Facts page.
References
Modeling evaporation of water droplets carrying virus particles
by Leonid A. Dombrovsky, Alexander A. Fedorets, Edward Bormashenko, Michael Nosonovsky
A video about aerosol vs droplet spreading of the new coronavirus: