The condescension only came from the worry that you would miss the forest for the trees, which you seem to have done unfortunately.

Yes, people do n fact sometimes say "man" for "a man." Perhaps your dialect may not allow it, but in my Southern Californian dialect, it's not unusual to hear an article dropped in regular sentences. "[A] Dude just passed by me smelling pretty rank." "[The] Lady just spat her coffee out everywhere!" "I wonder if [the] skateboard-guy over there can kickflip." "After going ballistic on that kid, [a/the] man just walked off like nothing happened."

This is not an unusual linguistic phenomenon as many languages can drop the determiner of any Noun Phrase and be fine. For example, most Slavic languages don't have articles, Latin doesn't have articles, and a language I did some research on, Hdi only used articles sparingly, seeming to prefer noun cases instead.

Language definitely is decided by at least a plurality - if not a majority - of a given population This is fact (see what I did there? No article!), and kind of the only way language can work. One or several people cannot come in an decide on a whim how language spoken by a much larger population will change- language changes by the population's (non-directional) whims only. Linguistic evolution parallels much in biological evolution regarding change.

If at least two people can mutually agree on and understand the meaning of an utterance, they have essentially created a dialect that is understood between them, and almost certainly mutually intelligible from whatever dialect they originated from. This is how dialects, sociolects, idiolects, and other -lects come about, and how language changes over time. This also happens all the time in large populations of speakers. But you can also cut populations up into subpopulations who also have dialects. For example, the Boston Accent, and the Bostonian Brahmin accents. Both are native to the city of Boston, but are accents which evolved out of socioeconomic differences - the Brahmin accent a subdialect of the general Bostonian.

And you're right about it not being decided by one person, ever - I had mentioned a small bit about that out as well...

For example, the "no split infinitives" rule is bunk: invented by a single man following the neoclassical movement during the Age of Englightenment.

Which is a bit odd as you seem to be deciding for entire populations what can and cannot be said, even though even you had just said otherwise:

no one, NO ONE, says "man" for "a man".

And you yourself prove what I had said in my previous post, anyways. If I may, bolding the important parts:

And the reason I understand what he said was because he later said what he meant to say and because I can tell that he left something out.

I had also said something about that, too...

Missing a determiner in this case does very little to alter the understood intent behind the sentence

and

You have some sense of comprehension [of the utterance]

Had you no sense of him "leaving something out," the sentence may as well read like Hungarian to a non-Hungarian-speaker, or like binary to an infant.

So anyways, you wanted some smug condescension? You missed the forest that was "Here's some information that may help you better understand this phenomenon, I urge you to read up on it some" (Though I admit, some sass was present because of the worry of just this event occurring) for the perceived trees of "this shall be a GRAVE insult to this stranger!" and "Wow, this idjit knows nothing about what he's saying!"

^{Your second post seems to prove that second tree as correct, however.}