But doesn't "sabbatical" just postpone the problem? After six months your friends will be asking the same questions again, no? Mine would be.
Maybe after a year or three, you could just say "this sabbatical is working out pretty well, I think I'll do this full time now". How much/little you reveal about your methods that allowed you to get to that point is up to you. If I knew the person well enough to know that they could comprehend and appreciate the effort it took to get to where you are today, I'd probably be forthright with how I achieved FIRE.
I have shared my secret FIRE plan with approximately 4-5 friends. So far, all are engineers, know how to use excel in depth, have taken engineering economics, understand compound growth rates and time value of money, etc. All are very financially responsible individuals. They see the big picture: work is not the be all end all in life; it is intrinsically valuable. It provides a paycheck that lets you buy nice things, pay the mortgage, save a little or a lot, and some day not have to work. Most are family or leisure oriented and appreciate having free time. These folks can understand what I am talking about, accept that it is a doable plan and an achievable goal, and recognize that it may be too extreme for their tastes but that it isn't unrealistic.
The vast majority of the remainder of friends/acquaintances/colleagues that I have would be unable to comprehend the relatively simple nature of FIRE (or I just don't know them well enough to know how they would feel). Hence no time is wasted being forthright with my big plans for the future. Explaining FIRE to most would be as cogent as explaining my rationale for joining a known cult or something similar. Life is too short!
Most of my social contacts are 30-ish so that shades my "proper conversation topics" as well. A lot of my friends and acquaintances are still in college finishing up a dissertation, doing a post doc, finishing up residency, or just getting started in a career. The rest have recently settled down, gotten married, bought a house, maybe popped out a kid or two. Retirement isn't on their radar and so my plans to FIRE would be a foreign concept.