Any bugfix could be seen as backwards incompatible in the strict sense "somewhere, someone might actually depend on this buggy behavior", yes. That’s not a part

Any bugfix could be seen as backwards incompatible in the strict sense "somewhere, someone might actually depend on this buggy behavior", yes. That’s not a particularly good definition of backwards incompatibility when it comes to bugfixes, however. A more reasonable definition is "requires changes to downstream code" as in the bug cannot be fixed without changing public API as well. That said, sometimes there definitely exist bugs that a lot of users factually rely on, and changing such behaviors should not be done in patch releases.