What’s the distinction between those two?
According to: https://kb.iu.edu/d/agat "To use the Unix trademark, an operating system vendor must pay a licensing fee and annual trademark royalties to The Open Group. Officially licensed Unix operating systems (and their vendors) include macOS (Apple), Solaris (Oracle), AIX (IBM), IRIX (SGI), and HP-UX (Hewlett-Packard). Operating systems that behave like Unix systems and provide similar utilities but do not conform to Unix specification or are not licensed by The Open Group are commonly known as Unix-like systems."
Many will include the *BSDs as a Unix, because their code does directly descend from the original Unix code. But Linux distros generally do not meet either definition of "Unix".
(It also seems odd from my perspective to call exactly only those two Linux distributions "UNIX" unless you're essentially using it as a legal qualification and not a practical one)
No one is claiming it can't be a Unix. But as you noted, Linux distributions normally do not meet the legal criteria, nor are they descended from one that did.
Legally Unix is a trademark and has a very specific legal meaning. If you don't mean that legal meaning, then it is clearer if you use another term. The usual term is "Unux-like"; that is the widely-used term and it has been for decades.
A rose by any other name may smell as sweet, but calling it a different word risks confusion.
Another part is the trademark and certification fee. https://www.opengroup.org/openbrand/Brandfees.htm
Linux is as much Unix as WSL1 was Linux - i.e. not at all, just clones.