The example you gave is not relevant. The researchers in this study are already directly contacting everyone they need consent from, and if an individual declines, the rest of the sample can still be studied (unlike in a classroom setting, where everyone's physically in the same room and it's impossible to study any of them in isolation).

Further, the study would still have worked if the researchers had simply asked for the information as researchers, instead of lying about their identity and making thinly-veiled threats of legal action if the subject doesn't comply.