So it is a weird example, since it NOT an example of a statement that is undecidable in every model.
These models can look very strange. For example, if ZF is consistent, then by the Second Incompleteness Theorem so is ZF + "ZF is inconsistent". By the Completeness Theorem, a model for this theory must exist. In this model ZF is inconsistent, so there is a 'proof' of a contradiction from the axioms of ZF. However, since we have assumed the consistency of ZF, such a 'proof' must necessarily involve nonstandard integers.