I remember that in the early days of the webcam - before I realized the value of what we were doing - we'd get the weirdest visitors, ostensibly to meet to see if they could 'partner' and under this guise they would ask all kinds of questions that would be none of their business.
Eventually I wised up to it, which is why my first response to you was that it sounds like competitors.
Keep your cool, make sure the people you work with (also in lower positions) know that you're under a mild form of attack. Especially front line people are prone to being 'pumped' for sensitive information.