You made some good guesses on what a pool genie is. Pool-naïf Bryan said, even if you didn’t know what a pool genie was, the line worked in context. I expected most people to know what a pool genie was, but I grew up in Orange County, near the beach, in a suburban neighborhood of the pool-haves and the pool-have-nots. But, far be it from me to create a literary stumbling block. (I used the word politesse twice in the manuscript and I got called out for that).
Yes, a Pool Genie is an automatic pool filter. The official Aqua Genie™ is built into the wall of your pool at waterline. However, I was referencing the portable filter that motors about the surface of the pool, vacuuming leaves and bugs and turds. Like an aquatic roomba.

When I was young, my friend Julia's pool skimmer looked like the SS Enterprise.
Today you can find a plethora of kid-friendly skimmers online.
Which I guess makes sense: if you’re a child, you could easily be terrified by the idea of Klingons trolling your pool.

Then again, maybe your child should have a healthy dread of the appliance. If it's powerful enough to suck up leaves, bugs and turds, it might inhale your bathing suit if you get too close.

These Dolphin brand skimmers look more like Panzer tanks. Notice the curious evolution of color: from Mac Classic taupe, to Trojan Pride, to Miami Vice, to the Miami Dolphins-sponsored Dolphin Deluxe.
Pool Skimming is Fun! At least that’s what the makers of this pool bot boasted. Notice mom and dad lounging contentedly, working on their skin cancer, while their Jonas Brothers son plays with what looks a robot catamaran."Go on honey, pretend you're James Bond and vacuum those ... (what are those floating in the pool Chocolate chip cookies?)

The most peculiar image I discovered while researching pool skimmers was this one.
It looks like something fished out of a camp lake in the Catskills.
But back to the book. The copy editor changed ‘pool genie’ to “automatic pool skimmer.” So the paragraph read, "Their front yards were fenced in and private, and when you walked past, you could hear the faint whisper of automatic pool skimmers and clinking highballs and success."
To me the change felt cumbersome and slowed down the line. It also took away the specificity of “genie.” For me a specific or brand name is much more evocative than a generic:
a) “You’ve got discharge on your shirt. Do you need a disposable handkerchief?’
b) “You’ve got boogers on your button-down, need a Puffs?’
And if the specific is too obscure, you lose the reader. I am considering a compromise: drop I “automatic” to speed up the line so it will read, “you could hear the faint whisper of pool skimmers and clinking highballs and success."
But now, if you read “pool skimmer do you think of this?

Or if you’re a guy, do you think of this?

At issue is either 1) literary integrity: should I dumb down my voice? Or 2) literary humility: Not everyone knows what a pool genie is Susan!! They’re certainly not going to abide reading “Politesse” twice. (I changed the second instance to
etiquette.) I am leaning toward "pool skimmer." Or maybe Jennifer's idea: a pool sweeper thingy.
If someone thinks of a pool boy, that’s the copy editor’s fault. I’m glad the copy editor didn’t change clinking highballs to “noisy alcoholic-beverage containers.”
And as for the roomba. I sorta knew what they were. Then I heard a podcast in which the speaker mentioned his roomba to a large audience and it got a huge laugh. Which meant that the Roomba has reached the Tipping Point. But Pool Genie may have jumped the shark.