Even with group interviews... Let's take the supposed profit, 300$, and assume it's 100 pops at 3$ each, and for the sake of it let's say revenue = profit in this case. That's 100 purchases per day.

The post claims 50 interviewees per day, so 2 purchases per interviewees.

By groups of 10, that's 5 cohorts spending 1h each with the interviewer, during which every. Single. Person. Buys 2 drinks?

Humm!