Airplane mode and clock setting

So this is funny. I went on a trip from Texas to California. On the way back, I set Airplane Mode on my iPhone, and forgot to undo that. I did not have cellular data turned on but, back home, I was well connected to my internet, got phone calls and messages and wifi notifications. But my clock was still on PST. So I turned off Airplane Mode and BOOM, clock was set properly. So Airplane Mode prevents clocks from being set. Evidently clock setting doesn't use internet, but uses data in some form, even though cellular data is turned off. Weird.