So, there are a couple of things. Here is where I push up my glasses and say "well--ahem--"
First, true, BSD is not itself Unix. That specific OS (which began with the PDP-7 Operating System in the late 1960s) really only existed until the late 80s or early 90s, when Bell Labs stopped working on it.
However, it is literally Unix-based. The first version of BSD was forked (as we'd call it today) from the Research Unix source code at UC Berkeley. Since then, the various BSD derivatives and distros have all iterated upon or forked from that initial Unix code. I don't think any are officially registered as SUS systems (but there are only a handful that are), which means that a pedant would say that BSD is technically "Unix-like."
But it is based on Unix, it's a part of the Unix family, just like Windows 11 is part of the NT family. MacOS is also part of the Unix family (I think it might be or used to have been SUS-registered, actually). Linux isn't, and I think I remember hearing that Torvalds didn't even use the Research Unix source code to write the Linux kernel originally, but it does follow a lot of the SUS spec and so is definitely Unix-like.