How are some people so comfortable asking strangers personal health questions?

I just got my dexcom a month ago and it's just surprising how many complete strangers ask about it ("what's that on your arm?" "Is than an insulin pump or something?" "Is that a nicotine patch?"), mostly customers at work. I don't really mind since I made the choice to put it somewhere visible but I would never ask a stranger something like that, it's weird how people are so comfortable. Has anyone else had experiences like this? This isn't really a rant or anything, just something that strikes me as odd.