I think this demonstrates the opposite of what you want. Saying "a hobbit hole is comfortable" would be telling. It's not explaining or showing what makes it comfortable, or why it is comfortable - it's one abstraction up and just declares it comfortable. For what we know at that point in the story, a hobbit likes worms and oozy smells and finds that comfortable.

But instead he evokes those images, and gets you to imagine something different; something probably closer to our idea of comfort, because the reader now has seen that hobbits ideas of what isn't comfortable is at least somewhat aligned with ours even though the live in a hole.

I'd consider this a fantastic example of how to show without having to be boring and prescriptive about just describing what you might see, but how you can also show through creating emotional response and through exclusion.

That said, good writers will know when to break the rule and tell. Tolkien certainly does tell a lot even if I don't agree that is an example of him telling. A lot more than many, if anything. But of course he gets away with that because he was a fantastic writer. The advice to show is beginner advice more than anything.