A peck is (was) a unit of measure, oddly. Same with a bushel. I know because my Grandma used to say "a bushel and a peck, and a squeeze around the neck!" to me when I was young. I had to ask her too.
Also, why would anyone she sell seashells by the seashore, of all places? Terrible business model to sell seashells where your customers can easily find their own.
From what what I remember, this saying is about Mary Anning and how she sold fossils by the beach in England where she lived. So most people probably didn't know how to pick a rock with a fossil, or open it well enough to preserve said fossil
So people say. I'm a bit sceptical about that origin story because fossils aren't seashells and, as far as I remember, Mary Anning didn't sell many of her fossils!
Next thing I know, you’re going to ask me how Moses could suppose his toes are roses. Cuz one might suppose that erroneously that anyone’s toes could be posies of roses as Moses supposes his toes to be.
I think you're on track. My best guess is that he was harvesting "pickling peppers" (i.e. peppers that would later be brined) and somehow the -ing ending turned into -ed. Probably for the sake of cadence in the tongue twister.
There is no capsicum fruit that grows in an already pickled state. Hopefully that's not a surprise to anyone. This video is a good overview of the varieties out there if you're curious though: https://youtu.be/BtsiuA7ETd8?si=rAUNaoQmDQvmLN_5