What does ‘Pinkie-sized’ mean?

It means "sized like the small finger"; it is generally used to refer to something that is small, in the same way thumbnail is used to means a small picture of an image.

The pinkie is the smallest finger in your hand. This is the one farthest from your thumb. The pinkie may also be called the fifth finger. Pinkie-sized means roughly the size of a pinkie (usually an adult pinkie).

Pinkie is an informal term used to refer to the smallest finger on the hand. Pinkie-sized is derived from that—something pinkie-sized is about the size of the average human's pinkie or smaller (it sometimes refers to just the distance between the last joint and the tip of the finger). It is not a technical term, and shares nothing relevant in common with the color pink (it may possibly be etymologically similar, but that has no bearing).

The pinkie is a primarily American term for the little finger, i.e. the one most distant from the thumb. (Note that native speakers of English would be unlikely to use the term small finger in this context.)