yep the rondel just means disc shaped, but there are other shapes that are historically used to protect the armpit. this specific piece of armor would actually be called a besagew (first post attachment is an example of a leaf shaped besagew as opposed to rondel shaped)

as for this fantasy piece of armor, I’m not sure if I could call it a besagew because they are usually just one big plate and not in an array, but it appears to functionally protect the armpits all the same. I guess the artist is trying to design their own take on scale mail?