I was much younger when I figured it out, but my mom also did a lot of gardening and canning when I was younger, so we had all kinds of pickled vegetables on the shelves.

There was still an aha moment when I realized that pickles were just pickled cucumbers, just like the pickled greenbeans, and pickled beets, etc.

I guess cucumbers were first on the scene and got to use the shortened name ;-)