I have answered this in the Matrix chat where this question was also asked, but for the sake of information being accessible, I'll also provide an answer here.
If your phone is in airplane mode and press the "emergency" button on the lockscreen (same thing applies after a reboot and after the first unlock), airplane mode is not disabled. You'd have to dial a number for that to happen, at which point it's not longer an accidental press.
Furthermore, the quick tiles to access Wi-Fi or airplane mode are inaccessible when the phone is locked, and you'd have to authenticate before they can be changed.
In general, yes, if you can make a call and leave airplane mode, you're talking to cell towers; that's how telephony works.
I would recommend reading this section of the FAQ in case you haven't at this point: