Have been wearing a mask since last week, which increasingly seems like a damn good idea.
Some important things to note:
They are droplets, not particles. This is an extremely important distinction in this case because large droplets can deform and be highly non-spherical. The deformation can lead to break up into smaller droplets and this field of work is called aerodynamic breakup. Particles are typically non-spherical, but they are rigid and less prone to break up, depending on the material.
Secondly, the are
not light. Particles/droplets which have a density which is significantly larger than the surrounding air (or whatever the surrounding fluid is) are called
dense or
heavy. Droplets in air are considered heavy. Light particles/droplets refers to a situation where the density of the particles/droplets are smaller than the surrounding air (or again, whatever fluid they reside in). The dynamics of heavy and light particles differ. You can usually ignore bouyancy forces for heavy particles/droplets, but not light particles/droplets for example. If the particles/droplets have the same density as the air, then they are called neutrally bouyant. The distinction is important because the research is sub-divided using this terminolgy. You will find papers which study "heavy" particles and others which study "light" or "neutrally bouyant".
Calling droplets "microdroplets", when exhaled via sneezing, when you have initially stated there are droplets with up to millimeters in size is misleading. It is better to say a "cloud" of droplets instead.
Most of the simulations with regards to the motion of droplets in air (multiphase flows) have issues. The majority ignore any coupling effects (i.e. they ignore any influence the droplet has on the motion of the surounding air etc and collisions between droplets). In this case, it normally isn't too important because you have so few droplets. We call this a
dilute air flow. Many will also lack modelling clustering mechanisms (where droplets get closer together in space and could make the dilute assumption invalid at these localised regions) and these mechanisms are already known to (via experiment) to change how quickly the droplets settle to the floor. Finally, when you give no details about how you actually carry out the simulation, you should really ignore the simulation part of the video full stop. CFD has lots of different pitfalls for modelling just air on its own, so you had better state the method before showing fancy videos.
The end bit, saying "the droplets can't move on their own" is incorrect. If there is no air motion, the droplets will still move because of the force of gravity. There will also be a bouyancy force and drag of course. They will settle to the ground and experiments to show their terminal velocity are
here. But yes, the smaller they are, the longer they will take to settle, and particles/droplets <20 micron are influenced partially by Brownian motion and this becomes more significant at <1 micron.
When they say "opening windows is believed to be effective" it is also misleading. Of course it is effective! Introducing any form of motion means that there are advective transport mechanisms (this means motion in bulk i.e movement across large distances rather than molecular motion) to move particles/droplets from one place to another. Ultimately this means the particles/droplets disperse through a large area rather than staying broadly within the same location.
The final bit, as to why the particles/droplets move, is related to something called the "Stokes number". This is a number which characterises effectively how well the particles/droplets move in the air. Since the small particles/droplets have a very small mass, they have little inertia. So when the air imparts energy to the particles/droplets, they offer very little resistance and are "happy" to move along with the flow. In this case, th particles/droplets have a very low Stokes number. Any such particle/droplet with a low Stokes number will follow well any air motion. This is well known for decades, it is nothing particularly new. The main challenge is that this Stokes number also depends on the size of the droplets as well as characteristics of the surrounding air. This means that a) it is not clear what the Stokes number is for a cloud of droplets of different size and b) you need to know some information about the air.
EDIT: I have ignored talking about evapouration because I don't know much about it but that will also be an important consideration.