The relationship between openEHR and ISO/CEN 13606 is a common question for newcomers, and sometimes a source of confusion.
As an overview…
openEHR and 13606 share a common heritage and make use of two-level domain modelling, based on the Archetype Object Model, which though developed by openEHR, is itself part of the ISO13606 specification. Both use archetypes to define their clinical content but openEHR and 13606 archetypes are quite different and are not compatible.
Their Reference models are quite different, and while sharing a similar high-level conceptual structure (Compositions, Sections, Entries, Elements) the details of these structures are very different, as are their datatypes.
These differences in part reflect the different scope and purpose of each - openEHR is primarily a persistence/query standard, whilst 13606 is primarily designed for data communication/exchange similar to the HL7v3, CDA and FHIR standards.
In summary, although ISO 13606 and openEHR have a common heritage, and share the Archetype Object Model, they each have quite different Reference models and therefore archetypes, based on the different requirements of a Communication standard (13606) and a persistence standard (openEHR).