Homekit: Is Openhab directly communicating with Apple? What is the communication workflow?

I intend to setup the Apple Home-Kit system integration for my OpenHAB system at home.
Accordning to the official OpenHAB documentation, the add-on basically exposes the OpenHAB system as HomeKit Bridge in the local network.
Only after pairing, the OpenHAB-controlled smart home devices will be exposed to apple, right?

But how does the rest of the workflow work? Does OpenHAB itself directly communicate with apple services? Or is it always the apple device (i.e. my iPhone / iPad), that communicates with apple on the one side and with the “homkit bridge” OpenHAB on the other side? Right now, I would assume the latter way…

And what about the scenario that I am away. Will my OpenHAB system at home be directly accessable via HomeKit (either because it is communicating with apple services, or, for example, another apple device is at home)?

I’m asking because it’s ok for me if data of my smart home infrastructure is stored at apple, as long as controll commands have to be issued from within my local home network and cannot come from outside without me noticing…

OPenhab exposes the items, and your apple home hub (an apple tv, homepod or ipad at home) are what expose the items to the internet allowing you to use them while remote.

When configured OpenHAB exposes your devices locally in your home network according to the HomeKit specifications. If you are just using an iPhone you will only be able to use the HomeKit integration as long as you are in your home network.
Additionally Apple HomeKit has an option to controll your HomeKit devices even when you are not in your home network (via internet) - for that you need either an Apple TV, an HomePod or an iPad which is permanently connected to a power source and in your home network: https://support.apple.com/en-us/HT207057