Great question and great chat earlier today! Well, yes in theory we are all related – if very very very distantly. I’m not sure on the correct science term, but it is a product of evolution. All current human beings are the product of a single evolutionary event a long long time ago.
I suppose that event led to one or maybe a few humans, and whatever we call ‘human’ now would have been in a very small number. That group then populated various parts of the world, and eventually, our species (homo sapiens) became dominant!
Of course, we still don’t fully understand the evolution of our species, but it is correct to say that all humans are distantly related, although that distance is now very very great! We are all the same species, and under the skin we are very very similar to each other!