Water bottle etiquette on the trail

The other day when I was running at Cedar Ridge Preserve, my hands got really cold, so I left my water bottle, which was full of ice and water, next to the trail.  I figured I would circle back to my car to get my gloves, then on my next loop on the trail I'd pick up my bottle.

With my hands warmer, and with a pretty good thirst worked up an hour or so later, I came back to that section of trail.  My bottle had disappeared.  Did I forget where I had left it?  Did some other thirsty runner pick it up?  Did the trail patrol throw it in the trash?  I didn't figure there was any way I had missed it, so detoured by the visitor center near the parking area and found it perched on the donation box.

The bottle and I were happily reunited, but it made me wonder about bottle etiquette.

Litter. Throw it away.

If I find a personal item like car keys or a wallet by the side of the trail, I think the best thing to do would be to take it back to the trail head.  Surely someone wouldn't leave something like that out on the trail intentionally.

Not litter.  Leave it there.

If I see an empty, disposable water bottle by the trail, especially if it's empty, picking it up and tossing it in a trash or recycling bin would be the reasonable choice.

But a nearly full, non-disposable bottle, with ice still in it, in a hand-held carrier?  I would not think someone dropped it and didn't notice.  I would not think that someone tossed it as trash.  The only reasonable explanation would seem to be that someone left it there intending to come back for it.  I detest trail litter as much as the next guy, but when something is clearly not litter, I leave it alone.

Am I right or am I wrong?  What do you think?