It is called "snowball sampling." While not a good technique to control bias, it does get plenty of data. This is likely an undergrad project with no budget allocated.
I participated in all sorts of studies at UWaterloo years ago, and always made a few bucks. Those were grad level studies, though. If I ever wanted opinion data for my own undergrad project, I was off to the mall or other place people gather to try to intercept people. There was no internet then, as we know it, so we had to pound pavement for data.