To me the most important part of that blog post is the bit about serendipity. Serendipity or spontaneous interaction is one of the biggest factors that determines relationships. I'm not sure if there's an official name for this theory, but I remember studying it in grad school. The gist of the study was that increased frequency in unplanned/spontaneous interactions was correlated with increased likelihood of a relationship (or maybe the correlation was with a stronger relationship).

Your friends from school are your friends because you had the opportunity to see and interact with each other every day, and get to know each other.

Same thing with romantic relationships. If you keep running into that cute girl or guy you kinda know, you'll have more chances to talk and to get to know them well enough to ask them out.

I think this is partly why dating apps have been such a crapshoot for so many people, they don't get the chance to interact past the initial swipe or chat. This is also partly why it's difficult to make friends as adults. You simply don't have as many opportunities to meet new people. And you don't have as many opportunities to turn those new people into familiar people and eventually friends.

Spontaneous encounters can only occur if you put yourself in a place for that serendipity to occur. So if you join a community like the blog post encourages, then you set yourself up to have more of those spontaneous interacts with the same people.