What did REPEAT really mean over an Army radio in 1965?

Exactly.
Repeat means repeat fire mission.
You didn't turn the target in to confetti mush, so drop more f you bombs on them to finish the job.

 

Repeat is to ensure there is a clear message conveyed.

someone would say "setting 123, repeat setting 123, over"

It was commonly used before FM was used in forward control situations and battle field operations.

I have training films (I moved them to Dvd recently) about military radio operations in WW2 and Korea and this is where my example came from.

 

As radio operator, I was schooled to NEVER SAY REPEAT except when calling for k indirect fire, ie mortars, artillery, naval guns, etc.
Repeat meant I want them to fire the same sequence of rounds at the same target.
Say again was used in lieu of repeat when you wanted the other unit to repeat what they said for clarity.
Ain't many things that say f you like a shake and bake mortar mission...
That's a few white phosphorus rounds with the fuses removed, followed by a few high explosive rounds to set off the wp.
Boom, flash, smoking hole in the objective area.
Brutal af, but effective in clearing out bunker complexes and the like... Tough to hide from that one.
If the explosion doesn't get you, the absence of air will.

 

I was instructed as @TNSquire has stated above.

 

After you wash and rince your hair...