no i meant in general... let me copy paste my explanation from sony thread
It's easier to show than explain.
Let take it from the "beginning"....
The AF-C setting is common across these.
1. a7RII/A7III/A7RIII (pre FW v3.0)
You had to set eyeAF to a separate button. When you pressed that button the camera did it's best to find the eye within the entire frame and track it. It simply ignored the focus area setting.
The focus area setting (simplifying it a little) ranged from wide area i.e. the entire frame, zones i.e. part of the frame and center/single spot which you can move across the frame. So half-pressing the shutter (or back-button) to focus would cause the camera to track whatever subject falls in that area. So in wide area while it's least accurate in terms of pinpointing the subject gave full frame coverage for tracking. On the other hand the centre/single spot gave you the accuracy for pinpointing the subject but you have to keep keep your subject on that single point for it to track and if left the centre spot you lose focus. The zone is a middle ground between the two.
To get over this limitation Sony provided another focus area called expanded flexible spot. So basically you get a central/single point, you find the subject with this point hence you get the pinpoint accuracy and should the subject move away from this point it'll track it across the frame thus providing the wider frame coverage. Win-win.
Notice how thus far eyeAF tracking and subject tracking are different things. Nothing to do with each other apart from both needing AF-C.
2. A7III/A7RIII FW v3.0
So they added real-time eyeAF (not the same as real-time AF, that's next). So in non-expanded flexible spot focussing area modes i.e. wide, zone, centre/single the camera will track the eyes as long as the eye(s) falls in the focus area. And if the subject leaves the focus area (bad in case of centre/single spot) it'll stop tracking it regardless of whether there are eyes in the frame. So for humans/animals i.e. subjects with eyes it can detect, setting camera to wide area mode (like in Nikon Zs) may work fine because it'll find the eye and when it can't it'll track something it thinks it should be tracking.
And in expanded flexible spot focus area mode you only got subject tracking and no eyeAF. Now you are back to above option 1 of setting a separate button for eyeAF.
3. "Full-fat" real-time tracking.
They replaced the "expanded flexible spot" with a "tracking" focus area option. In this option you point the centre/single spot at your subject and it'll track that subject. Should the subject have eyes it'll track the eyes (regardless of whether your point was on the eye or not) and if it doesn't find eyes it'll just track the subject across the frame till it sees the subject's eye again.
You can still of course map a separate button to do eyeAF still but it's not needed anymore.
A7RIV has 3rd version for humans and 2nd version for animals. A9/ii, A7C, A6100/6400/6600. has 3rd version for both.
Makes sense?