I'm pretty pro-Git, but I agree with the author on the wording of that message (though I disagree with their suggested alternative). "Your branch is up to date with ‘origin/main’" is technically correct, but the usage of the phrase "up to date" implies on a casual reading two things: That main matches origin/main, and that origin/main is up to date (i.e. that it was updated as part of the command, or is being kept up to date automatically and the last successful sync was arbitrarily recently). We're talking about a user-facing status message, not a machine-readable signal that must be true during this CPU cycle. This is a reasonable interpretation without having to get into networking theory.
"Up to date" means caught up in time, as opposed to space. Local branch positions are more like space ("where is this branch pointing?") and remote ref state is more like time ("when did I last update the remote ref?"). I know, that's very subjective. Either can mean either.
Anyway, I think a better wording might be "Your branch matches origin/main" or "Your branch's head is the same as origin/main" or "Your branch is pointing to the same commit as origin/main" or some other tradeoff between verbosity and clarity. Maybe with the author's suggestion as a parenthetical: "Your branch ... origin/main (remote ref last updated 5 days ago)."
"Up to date" means caught up in time, as opposed to space. Local branch positions are more like space ("where is this branch pointing?") and remote ref state is more like time ("when did I last update the remote ref?"). I know, that's very subjective. Either can mean either.
Anyway, I think a better wording might be "Your branch matches origin/main" or "Your branch's head is the same as origin/main" or "Your branch is pointing to the same commit as origin/main" or some other tradeoff between verbosity and clarity. Maybe with the author's suggestion as a parenthetical: "Your branch ... origin/main (remote ref last updated 5 days ago)."