I agree with the main conclusion of the study, i.e. if everybody used masks it would reduce the spread, but not necessarily with the conclusion that viral particles in the air are more important than on surfaces. It is not surprising that if they take samples of victims breath it will have a high virus load but what happens then? Does that spread out to a great distance or does it quickly settle on surfaces? How much of the virus load is in droplets and how much in aerosol form.
It has always been known that the virus is expelled by coughing, sneezing, although sneezing is not a common symptom with COVID-19, speaking and even breathing. Mostly that is in droplets rather than aerosol form. As far as I can tell a virus cannot be carried by a molecule of oxygen or nitrogen? It is carried by moisture. Aerosols are simply much smaller droplets and so cannot carry as big a virus load as a larger droplet. The droplets quickly settle out of the air within a short distance of the person expelling them, hence the 2 m distancing rule. It's not a cliff. You are not in a cloud of droplets at 1.9 m and then in clear air at 2.1 m. The number of droplets decreases as you move away from the person expelling them so the risk of infection decreases. The figure of 2 m is seen as an acceptable level of risk. Aerosols will travel further in the air than larger droplets but they contain less virus. This is direct infection and is the highest risk for doctors and nurses treating COVID infected patients because they have to be close to them. It would also be a high risk for ordinary people in confined spaces but I don't think it is the highest risk for most people as long as they stay more than 2 m apart.
Obviously the droplets settle onto surfaces where they can live for some time depending on the type of surface, e.g. up to 72 hours on hard surfaces like metal or plastic. Other people then touch those surfaces and subsequently touch their face transferring the virus to a point where it can infect them. This is indirect infection and I think it is the highest risk for people who are not in close contact with COVID victims, hence the rule to not touch your face and wash your hands thoroughly and very frequently. It is an especially high risk in places like public transport where everybody is constantly touching the same surfaces, handrails, seats, buttons etc.
Wearing a simple face mask will not protect you very well from catching the virus by the direct route since the virus can get into your system through your eyes as well as your nose and mouth. You would need to wear the sort of mask that doctors and nurses in ICU wards use with a large visor or tightly fitting goggles. In fact wearing a simple face mask may increase your risk of direct infection because it makes you feel safe so you are more likely to ignore the distance rule and hence droplets are more likely to get onto you, your clothing and the mask itself. Unless you follow operating theatre procedures for putting on/taking off the mask you can then get contaminated. It may also increase your risk of indirect infection because you are likely to be touching it all the time and you can then transfer virus to your face from objects that you have touched where droplets have landed. In general unless used under medical conditions with adequate training a face mask is not very good for protecting you from infection from other people.
What a mask over your nose and mouth will do quite well is drastically reduce the amount of virus you are expelling into the air if you happen to be infected but don't realise you are. Therefore it is pretty good at protecting other people from you. Since we don't know who is infected and who isn't it requires everybody to wear a mask, especially where distancing is difficult. This is what people in the east understand, partly because they experienced outbreaks of SARS and MERS, and nobody in the west can seem to get their head round. If everybody wore a mask in all public indoor spaces the rate of infection would go down drastically. If only a few people wear them it will do very little. If you look at China, South Korea, Japan, Singapore, Taiwan etc virtually everybody is wearing a mask at all times. If you look at the UK and Greece virtually nobody is wearing them whatever the situation. Either the western governments are not communicating the message very well or we couldn't care less about protecting other people we are only interested in ourselves?