Roman Full Plate Armor?

[D B Campbell]

If this isn't mickey mouse, what in the world is it? ... we humans are a bit too eager to link a known image or idea to something that resembles our preconception of the idea.

You nearly had us there, Endre.
(1) The statuette looks like Mickey Mouse.
(2) But Mickey Mouse didn't exist back then.
(3) Ergo, the statuette can't be Mickey Mouse, so we are permitted to write it off as unintelligible.

In the case you are discussing, the argument runs like this:
(1) The statuette depicts a heavily armoured man, who doesn't look like the usual types of armoured men we are familiar with (legionary, auxiliary, etc.), but might be a known type that we are unfamiliar with (crupellarius).
(2) Tacitus was a contemporary observer, and describes the crupellarius as a particularly heavily armoured man.
(3) Ergo, our statuette might be a crupellarius, or it might not be a crupellarius, but we can't write it off as unintelligible.