These interviews are standard for most flights to the US, and are mandated by the US government. Although similar rules have existed for several years, the latest round were announced in June of 2017, and came into effect 120 days later.
Although these interviews are mandated by the government, it is the responsibility of the airline to carry them out. In most locations the airlines will use some form of security staff to carry out the interviews, however it’s certainly possible that other airline staff are used in some locations as you’ve stated.
As far as I’m aware, the exact requirements for these interviews is not something that is publicly available.
Credit:stackoverflow.com‘