this is likely in reference to the fact that dicts have maintained insertion order since Python ~3.6 as property of the language. Mathematically there's no defined order to a set, and a dict is really just a set in disguise, but it's very convenient for determinism to "add" this invariant to the language.

Not related to Python, but one of the possible implementations of a set, i.e. of an equivalence class on sequences, is as a sorted array (with duplicates eliminated, unless it is a multiset, where non-unique elements are allowed in the sorted array), as opposed to the unsorted array that can store an arbitrary sequence.

So sets can be viewed as implicitly sorted, which is why the order of the elements cannot be used to differentiate two sets.

Being sorted internally to enforce the equivalence between sets with elements provided in different orders does not imply anything about the existence of an operation that would retrieve elements in a desired order or which would return subsets less or greater than a threshold. When such operations are desired, an order relation must be externally defined on the set.

So a possible definition of sets and multisets is as sorted arrays with or without unicity of elements, while sequences are unsorted arrays (which may also have the constraint of unique elements). However the standard set operations do not provide external access to the internal order, which is an order between arbitrary identifiers attached to the elements of the set, which have no meaning externally.

A stable order does not imply sorted order. If you convert the same set to a list twice you'll probably get the same order both times but it isn't guaranteed anywhere, and that order may change between python implementations and versions. The order may also change as the set grows or shrinks.

So are dictionary keys, but Python decided to make them insertion ordered (after having them be unordered just like set elements for decades). There is no fundamental reason sets couldn't have a defined order. That's what languages like JavaScript have done too.