It is not reasonable to claim this prefix unambiguously refers to the OpenBSD team. I do not understand why so many in this thread are pretending this isn't a confusing choice.
In fact, your insistence that “Open” can only be used by projects that are replacing proprietary software is itself very odd.
OpenBSD itself has had its name for thirty years, and is not named for being an “open source” implementation of a proprietary OS.
Do not invent arguments that I did not make. I have only said that naming it openrsync when rsync already exists and is "open" in the general sense is confusing.
I find the negative reactions to this observation very confusing, especially yours, but I see that you're an OpenBSD developer so that explains your bias.
Edit: and now these same people are backtracking to agree with me that "open" is ambiguous, this place never ceases to amaze
What was said is that the OpenBSD operating system folks chose to use the Open— prefix for all their other projects ("They simply ran with the naming convention."). What was not said was that all Open— prefixed projects were from them.
Not closed source, but with rsync 3.0 it changed its license to GPL3, which a lot of folks don't like: BSD/MIT licenses have zero limitations on use and distribution, GPL2 (rsync 1.x, 2.x) forces one to release code, GPL3 (rsync ≥3.x) adds further restrictions.
Some folks want to distribute code with as few restrictions as possible. Other folks have a great good/goal in mind (e.g., 'all software is open source') and so add 'local restrictions' to hopefully achieve greater non-restrictions.