The era of finding one company and making one's home there, for the duration of a career, is pretty much non-existent in the private sector at the present time, though, it does occur, but not very frequently. So too, salary reviews, and annual bonuses, are something that most employees discover, seem to be less about a real review and merit, but are instead, more about a predetermined salary increase, that is usually within a very narrow incremental range. This means, more times than not, that those wishing to make a substantial or meaningful increase in salary, no matter how competent, are probably going to have to seriously consider looking for another job, and negotiating from a higher level from the get-go.
Not too surprisingly, to a very large extent, the absolute best company to try to find new employment at, would be a competitor of your current company, because of the knowledge, pertinence and experience that you bring to the table. This signifies, that when you are contacted by a competitor, most people, unless they are completely satisfied with the current employment, are going to have a tendency to want to look them up, especially if they are dissatisfied with their current setup, for here is a chance to not only to make more money, but also an opportunity to advance.
The thing about an interview, is that most people want to put their best foot forward, of which, not only should they want to, they actually should. So too, in order to help prove your worth and value, the interviewee, is almost for a certainty, going to have to talk in specifics about what they currently do and specifically address it in a manner that demonstrates that they actually know what they are talking about.
Additionally, people that are nervous, or are put on the stage, so to speak, have a tendency to talk more, than perhaps they desire to do so, especially if the recipient of the information, is either quite good at looking unimpressed, or asks just the right follow-up questions, which brings out even more information.
The unfortunate thing about life, is not everything that appears to be what it is, is what it is; of which, some competitors, deliberately want to bring in some of the best and brightest from the competition for an interview, not necessarily to hire them, but rather to learn about what those competitors are actually doing, thereby essentially utilizing the interviewee as a mole, to extract actionable information from. While, of course, this is quite unethical in every conceivable way; it isn't illegal, and the information being so provided, can be of immense value to the company of the interviewer.
So yes, not every interview is an interview, of which, some of the fault lies with the present company, that isn't doing all that they could to keep their good employees engaged and properly rewarded; while most of the fault comes from the competitor, that rather than concentrating of getting their own house in order, take the shortcut of finding out, rather underhandedly, what the other guy is doing, by using the interviewee as their pawn to be debriefed.