Is a Non-U.S. organization developed software model of a U.S. export controlled system also export controlled under U.S. regulations?

If the model uses U.S. export controlled technical data that reflects the performance or capability of the U.S. export controlled component then yes, it would be considered export controlled, even if the data is produced by the Non-U.S. organization. It doesn’t pass the logical test that it wouldn’t be export controlled either. Data produced by a Non-U.S. organization is typically not export controlled but when it reflects the performance and capability of an export controlled system then it would be.