It's RPC. Remote procedure calls. An approach that has made a comeback in the front-end space recently. There was tRPC; then react made a splash with the release of its server components; then other frameworks started emulating the approach. I think Svelte now has something similar with its "remote functions". And Solid has been working on something similar; so that SolidStart now has a "use server" pragma. They probably don't replicate React's protocol; but the idea of calling functions on the server is similar.
It wasn’t really a “comeback,” RPC never lost popularity. We just called them “REST” APIs that were a barely disguised adhoc JSON RPC format with a few CRUD verbs tacked on for routing requests.