Which established mechanisms does the Feynman technique combine?

It operationalises self-explanation + retrieval practice + learning-by-teaching in one routine.

The Feynman technique is best understood as a branded package of ingredients that are each independently supported. Explaining in your own words is self-explanation. Doing it from memory is retrieval practice. Framing it as teaching invokes learning-by-teaching. The evidence for the branded package as such is light, but each component is well-studied — so the honest assessment is "strong components, lightly-tested bundle." You're not relying on faith in a hack; you're stacking three techniques that work.