Каждый коротышка был ростом с небольшой огурец.
I am translating it as every small person was of the size of small cucumber?
I am confused about the case, why is cucumber in accusative or nominative and why use с небольшой?
1 This is one of adjectival constructions in Russian to denote likeness in terms of measures.
размером с горошину
as small as a pea
ростом с мизинец
as short as a pinkie
весом с пудовую гирю
as heavy as a 16 kg weight
рептилия длиной с автобус
a reptile as long as a bus
глубиной с Марианскую впадину
as deep as Mariana Trench
толщиной с бревно
as thick as a log
шириной с футбольное поле
as wide as a football field
In these the preposition C governs Accusative case because it implies a question c кого? с что?
An approximation of literal translation would be
but a more idiomatic one is
A word denoting a type of dimension or quality (размером, высотой, шириной, длиной etc) can be omitted if it's clear from the context
величинойс пудовую гирю
2 Instead of небольшой one can use маленький as well. But in this context these words differ in their register. Маленький could be perceived as belonging to a primitive language, like that of children and poorly educated speakers.
"Небольшой" is perceived as slightly bigger than "маленький", but not yet so big as "big". Think "medium or just a tad bigger".
And "коротышка", being the quasi-race name, would be better translated as, e.g., "shortling".
Each shorty was as tall as a small (standing) cucumber.