So because he knows only a limited amount, that’s the distinction between private and anonymous?

It is my distinction, yes. There are many other distinctions like it, but this one is mine based on my threat model. Now, if you'd supply your definition/distinction and threat model, then I can be pedantic about it as well. Or we can accept that, since we are talking about a wide swath of users, no one real definition suites all. If you'd like a similar exercise, hit Lemmy Self Host and pose the question, 'What is self hosting? Is hosting on a VPS considered self hosting or is a home lab considered self hosting'. Report back please.

Signal is not your neighbor. Signal’s DB stores phone numbers and knows who you are, and who you talked to, and when

You know the part in the Signal setup where it asks you for your phone number for verification purposes? You do know Signal does not prohibit the use of temp phone numbers. You can try as many as you like until you get one to work (if you're relying on free temp phone) One phone number not giving you any joy, tap 'Wrong number' and try again, or use a paid for burner phone service such as MobileSMS.io (which is specifically recommended for Signal), Burner, Quackr.io, Temp-Number.com, or there are reports of using Google Voice, if you dare tread those waters.

As clients upgrade, messages will automatically be delivered using sealed sender whenever possible. Users can enable an optional status icon that will be displayed in the detailed information view for a message to indicate when this happens. These protocol changes are an incremental step, and we are continuing to work on improvements to Signal’s metadata resistance. In particular, additional resistance to traffic correlation via timing attacks and IP addresses are areas of ongoing development. https://signal.org/blog/sealed-sender

As I understand the Sealed Sender protocol, it does redact or seeks to redact the metadata of 'whom you contact and who contacts you'. Since 2024, Signal has introduced usernames to reduce reliance on sharing phone numbers. You can set a username and hide your number from others, though it remains in the database for account purposes. Sooooooo....find you a temp burner phone number to use.

As I've said early on, I have no dog in this hunt. You can use Signal, Simplex, Smoke Signals, design a new enigma machine, whatever. My corn is going to grow regardless and my neighbor will still not know about my sex dungeon and crack still. LOL