For example, on some android phones, the data connection shows as on when you are on a call, even tho apps cannot access the internet.
So I'm assuming the OS just built a workaround that turns data on only for calling, since if data is allowed to be completely off, people are gonna be complaining that their "Phone isn't working" as most carriers require VoLTE these days.
Same thing with location. Even if you turn location off, it is automatically turned on if you call emergency numbers.
When you make a phone call, the antenna's are used 100% for calling and using data is disabled (or at least, it used to be). Android might thus "pretend" that it is still connected.
Data is definitely usable when you make a VoLTE call. But if you turn data off before the call happens, the data icon on the top quick setting panel where you pull down on the notifications indicates that data is "on", and attempting to turn it "off" would show a message saying "Unable to turn off data while Advanced Calling is on" Advanced Calling which I assume means VoLTE. So basically its this state where its on, but only for the purposes of VoLTE. If you have data set to on before the call happens, you can look up info while, for example, you talk to a customer service representative.