It depends on your definition of what a gherkin is.
Some say that gherkins have to be pickled to become a gherkin, as it’s an integral part of the process. An unpickled gherkin is just a cucumber to people who believe this.
However, there are some gherkins that exist, such as the Cucamelon or Mexican sour gherkin that will allow you to technically be eating a gherkin without having to pickle it necessarily.
It’s really a matter of semantics and language getting confused over time.