The thumbs up/down is simply a bad metaphor because it’s commonly associated with like/dislike.
What it really does is giving you an option to add the next track to the queue or not. Think of it this way and most of the confusion will go away.
Of course, you may still not know the next track, but that can’t be helped in radio. If you do know it, you can decide to not put it on the queue if you don’t like it. If you don’t know the song, let it play and then skip it if it turns out you don’t like it. Then Roon will ask why you skipped it. (Apparently with the limitation as described by Geoff in the previous post)
Somewhere in the many times this has been discussed, a Roon developer acknowledged that the thumbs metaphor is confusing and should be changed:
https://community.roonlabs.com/search?q=radio%20thumbs