There are lots of currently very successful startups that were not at all profitable at 2500 employees. The question by itself isn't a particularly good way to gauge the health of a venture-backed startup.
Another reply mentioned unit profitability, but do you have any other specific questions you think would be better to ask?
At a 2k+ person company? I doubt the interviewer would know much more about the business than what you can find online. It certainly makes sense to try to figure out the health of a business you're considering taking a job at. I'm less sure your interviewer would be a great source for that kind of info, though.