Without seeing pictures, I'm not sure anyone can say for certain. Maybe it means "low elbow"?.... meaning you are dropping your elbow as your hand is about to enter the water, rather than having a high elbow (keeping your elbow higher than your wrist).

I don't know about the "big overhead windmill style"... there are different stroke types and styles, but not really any perfect stroke. Maybe they mean they want you to have more clearance of the water in your recovery, rather than swinging it out wide. Check out Swim Smooth for some examples (or search youtube) for stroke styles.

Likely means your body roll is either sub-optimally reduced, or your timing of that roll is off. I see low arms in people with flat strokes where trunk doesn't rotate much around a long axis, or they roll early when the recovery hand is passing the head and don't wait until it's entering the water. Maybe...

Bu itself, it doesn't really mean anything. Is it both sides or just one, or just your non-breathing side? Is it causing other issues with the stroke? Is it a symptom of not rotating enough? A big overhead windmill isn't necessarily desirable either, as it could mean you're wasting energy to lift all that mass so high every stroke. Or not....

There are a LOT of individual variations on the recovery portion of the stroke. It really comes down to whether the recovery is causing issues under the water.

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Apparently it’s both arms. I asked if other issues were visible from above water and none were noted, so that’s good. I agree that a big overhead recovery looks pretty but isn’t a true measure of efficiency in terms of energy savings. I guess I have the ugly triathlete swim stroke.

Open water swimming stroke is a little different than a pool stroke. I am, and will always be, a pool stroke swimmer.
Open water stroke tends to be the higher (so you don't get caught up in chop) windmill style

This https://www.youtube.com/...5Jj9IUWkc&t=127s explains it better.

Mind you, if you are a good pool swimmer, you will still do fine, just not super fine......