leather cuirass

[Dan Howard]

The very least, "it is" a cuirass, and "it is" not made out of metal.

Depends on how you define "cuirass".
The word comes from the French cuir, which means "leather" and originally only referred to leather armour. There is no way to tell what the sculpted item is made from so, no, we can't say that it is this kind of cuirass.
Later the word was expanded to include metal armour. It is unlikely that this is made of metal so, no, we can't say that it is this kind of cuirass.
If you mean "cuirass" in the most general sense to include costumes that may not have even been intended for battle then, yes, you can call it a cuirass.

I wouldn't use the term cuirass unless it was intended to be used in battle (i.e. "armour" not "costume") but it all comes down to semantics. When writing about these subjects you have to firstly define all the terms you are going to use since many are arbitrary or ambiguous. Otherwise the reader has no idea what you are talking about.