

It shouldn’t be, no. But one of the big problems with phones currently is that the radio firmware is almost always a closed-source binary blob.
Airplane mode is probably better understood as the OS asking the radio nicely to not attempt to communicate with the outside world. The antenna is still there able to receive signals, and the radio technically doesn’t have to listen to the OS if it doesn’t want to.
It’s incredibly unlikely (researchers look for this kind of thing), so make sure your tin foil is on tight, but not impossible that a radio could store cell tower identifiers it has seen whilst on airplane mode and do something with them when it is allowed to communicate again. There’s also the possibility there’s some secret signal that can be sent to force a phone in airplane mode to respond.
Unless you’re up to some Edward Snowdon level stuff though, even if that last one exists, it’s probably not being used on you.
That looks like a pretty cheap subscription fee for a country ~25%.
Mine is closer to actually half, though we get healthcare and a half decent social safety net with ours.
Happy to pay it because I know I’d not be where I am now without the stuff taxes pay for