IKEA pairing somehow different than Zigbee binding?
Ikea pairing is Zigbee standard group binding via touchlink initiation. What is different is Home assistant, which doesnt really handle Zigbee groups.
But I'm also curious about the option in Home Assistant to bind devices.
If you mean zigbee group binding, in my experience Home Assistant doesnt handle Zigbee groups well. There is technical capacity and group manager, but to me it seems it doesnt correctly bind all of the action clusters and so on. Plus most finally the UI is very confusing etc. (That or I'm dumb and can't get it working right)
Home assistant handles grouped devices primarily inside its own logic and talks to them as individual devices. Which leads for example to stuff like non synchronous action. I don't think Zigbee groups either guarantee synchronicity, but it is pretty instant since it is single mesh wide broadcast of "whole group this, do this". Where as Home assistant send say ten different messages to ten different Zigbee devices. Thus there is delay and difference, when each device receives their individual command.
Most dedicated Zigbee hubs like trådfri and hue use actual Zigbee groups. When moving devices between "rooms" or whatever each call it, it sends actual configuration message of "change your internal registered group identity" to the lamps, remote controls and so on.
Insurgencency operation math: 10 insurgents before - 2 killed insurgents = now you have 20 insurgents