Well I mostly agree, one issue is putting your phone in airplane mode does absolutely not mean it’s disconnected (neither is turning it off, or the battery running out in many cases e.g. iPhones still communicate with the „Find My“ network when your battery runs out or you turn it off). Also, most phones still have reception even when you don’t have a connection because for stuff like emergency services your connection is routed over ALL cell towers, not just the ones of your provider. So if you see no bars it doesn’t mean you’re not communicating with a cell tower.
So to be off the grid the way they’re talking about is removing sim + turning it off, or removing the battery. Both of which are rather drastic for „wanting to be left alone“.
I’m not trying to defend their assumptions, I’m just saying their „that person is offline“ is more meaningful than just „he’s not receiving my iMessage“ or whatever.