Eggplant......I'm envious. I've tried to grow eggplant, but they come out long and slim, like a skinny cucumber.
I like to grow the long, slender ones (Ichiban) as I get more out of them, they just keep producing. The big plump ones (Black Beauty) it seems I get a lot of plant and a few big fruits and that’s it.
The bitter melon is in the cucurbit family, like cucumber, squash and melon, so I guess it technically is some type of melon.
Maybe you unknowingly planted an Asian type of eggplant? Those are usually long and thin. The kind I planted is Black Beauty. I got lots of fruit from the three plants I put in. They love the monsoon season here in Phoenix.