Could it also have made sense to call it a "Form", as in the Platonic sense of the ideal form that represents the thing which earthly objects strive to emulate?
Just did some googling and it seems the terms were invented by Ole-Johan Dahl and Kristen Nygaard for their Simula programming language
We chose the terms “class” and “objects” of classes for our new Simula. The notion of subclass was especially appealing to us, since we had seen many cases of objects belonging to different classes having common properties.
The main impact of Simula 67 has turned out to be the very wide acceptance of many of its basic concepts: objects, but usually without own actions, classes, inheritance, and virtuals, often the default or only way of binding “methods’’ (as well as pointers and dynamic object generation).
Because 'class' is a great choice for the concept?
"A set or category of things having some property or attribute in common and differentiated from others by kind, type, or quality."