When they say that to me and my empty plate, I always respond, “I didn’t like it at all”.

Maybe the restaurant was playing a recording of Sammy Davis, Jr, singing "The Candy Man" song, where "you can even eat the dishes" ?? Haha!

Many years ago my wife and I in Rome decided by the time we really should eat. But we'd been walking and snacking all day so we were more tired than hungry so we just ordered one meal between us to share.

The waiter, whose English wasn't great but much better than our Italian, decided we were being frugal because that was all we could afford. A couple of minutes later he came back with two big bowls of tasty lentil soup. All he would say was "Just to try, just to try."

I suppose waiting, especially in a tourist city, has to be a big collection of judgement calls. We liked the soup and the waiter so we ended up 'buying' the dinner with the tip. But it was a judgement for us to avoid insulting him while making the situation right. At least it was a pleasant situation for everyone involved so it seemed to come off well. When you barely speak each other's language it's easy to run into minor misunderstandings. Ha, ha.

My mother, who finished HS in 1923, said waiitresses were told to entertain customers. For instance, a customer who asked for two poached eggs on toast heard her ask the cook for “Adam and Eve on a raft”.

I worked as a waitress for many years, we were in Every establishment told to never remove a plate without asking Unless the utensils were placed across the upper right corner of the plate parallel to each other and the center of the plate (sort of between 11 and 3-4o'clock) as a sign the person was finished. They might be awaiting a portion of food from another diner at the table, and Nobody wants to eat off another's plate using their utensils.
Your server was properly trained, even though many diners nowadays have no idea what they are doing.....

Now I'll have to get one of them fancy watches with hands.

"When you've finished a course, you should place your utensils (typically a fork and knife) on top of the plate. Most etiquette guides use the clock method to explain the exact placement, with the handles of the utensils placed at 4 o'clock, and the tines or blades oriented diagonally to 10 o'clock."

That's a pretty standard phrase to say before taking the plate. Unless it is on the side of the table not in front of them anymore them.
Sometimes people are keeping the plate to scrape off the bits or if someone else is with them they might share. Or maybe you have some candy in your pocket for dessert.
Never ever assume someone is done with their plate if its in front of them. People don't get that and a good potion of them talk down to the staff or make jokes insinuating they are unintelligent when they ask.. but it's better than taking it if you aren't done with it.

Long ago, I was out to dinner with my husband and kids. The server went by, picked up my barely half-eaten salad (main course, not the appetizer) and walked away with it. I looked at my ex in amazement and he was also perplexed.

She didn't come by again except to drop off the check and hurried away before I could say anything. When we checked out, she was the cashier. I told her that I had not finished the salad and should not be charged for it. She stammered out that she couldn't do that and I replied that the manager could. She stammered something about the manager not being in. We paid for the dinner but left no tip.

We never saw her again in the restaurant. I was not surprised.

It's always better to ask even the obvious questions. Lest someone accuse you of committing a social faux pas!. Common sense is not all that common..I can just see some xtian.getging but hurt because they didn't get time to give it a proper blessing.