How my Applewatch(Series2/Ver.4.2) is connected to my iphone without Bluetooth, Wifi, cellular connectivity?!!

Hi Guys,

I just saw my applw watch was connected to my iphone without turning on the bluetooth over my iphone7(11.2.2), i could able to control the music feom apple watch. I was not connected with the wifi as i was on celluler.Then for the test i stopped celluler and still i could use the music app through applewatch. Obviously, i’m missing some info here on how applewatch is connected without turning on bluetooth, wifi, celluler connectivity?

Pls fill me in. Thanks in advance