But the original statement is still a false statement, is it not?

If others are free to observe you while you are in public with them, are they not also free to do whatever they wish with that information? Same as you are free to attempt to share as little as possible with them. Public spaces are commons, and private spaces are subject to the rules of their owners, as you are also bound by them, in some form.

Once you leave your own property, what you do ceases to be your business alone, and begins to also be someone else's. There are clearly matters of degree, but it's also impossible to be in public without broadcasting copious amounts of personal information. If others in public are equipped to collect that information in whatever form it takes, why is that suddenly wrong?

Disagreeing with that tells me that by saying "my business is only my business, and nobody else's" you really mean "no one has the right to observe me/interact with me in public". Otherwise, you'd have to agree with my earlier statements, right?