A couple times I've caught myself saying "I know a person who..." when what I meant to say was "I follow a person on Instagram who..." It was really eye opening.
I've found myself doing the same thing. But you can work next to someone in a cubicle for years and know less about them than you would from subscribing to someone's blog (assuming it's honest). I value in-person interaction, but I've also gotten to feel like I know people with whom I've only interacted with online, via email and MUDing back in the day.
How well you really know someone is hard to quantify.