Yes, there is curiosity. I'm not sure if that proves the point that one would not want to reveal details about the business, or if it indicates that perhaps the commenter's claim strikes many people as somewhat outlandish, or at least rare. I'm sure there are some folks out there clearing $4M/year with their bootstrapped business. But I'm also sure there are folks out there who tell tall tales on the internet.
Take a look at any sub-reddit related to entrepreneurship. The minute someone even hints they are making a lot of money in some area you see multiple replies asking about the product, niche, etc. People will clone what works. Why would anyone create that kind of exposure if they didn’t need to?
[Edit: just read the rest of this thread and there are three people asking the $4 million guy how he did it, so I guess point proven?]