AFAIK it remains unknown how many viruses are required and where in the human body to get an infection. So 'quantities large enough to be infectious' is probably false.
There are very well defined scientific protocols for what an infectious dose is, used in this research. You can put your “probably false” argument against the contents of the paper.
I was not referring to anything like that, but to the fact that a different amount of different viruses is required to cause an infection. E.g. in this paper it is estimated that influenza A (in aerosol form) requires around 2000-3000 viruses to infect: https://www.hindawi.com/journals/av/2014/859090/#conclusions. On the other hand Noro-viruses can infect a person in much smaller quantities (don't bother finding a reference but you'll find it quickly). All I'm saying that it's unlikely that we know such numbers at this point for SARS-CoV-2 so in the paper you linked they must have used some other definition for an 'infectous dose' than what you'd intuitively think.
Edit: Now that I actually read the paper that OP posted, it seems that they're estimating the half-life of SARS-CoV-2. It really depends on the initial amount of viruses how long it takes to go below some fixed 'non-infectious limit'. So numbers such as '3 hours' quoted in the paper are pretty much meaningless in practical situations where the inital amount of viruses might be much different. It's not that they're trying to emulate a cough or something.
