Originally Posted by Tchiowa

You put it in a pocket of a seat where you weren't sitting and are surprised someone else took it?

It's common for airlines to pass out bottles of water (depending on airline, length of flight, etc.) so it's easy to see that the other passenger thought that's what it was.

Stern looks and stink eyes should be aimed at the person who tried to confiscate part of another seat by putting his water bottle in the pocket.