People have made friends without college for millennia. I also don't see college as uniquely powerful in that regard. A compelling case could be made that college is less likely to lead to deep bonds than serving in the military is, for example.

I'd also say that things like coding bootcamps or intensive language schools are fantastic places for making friends—largely due to the greater number of hours per day and the greater intensity of effort involved than in a typical college experience. Intense startups can also have this feature.

We can agree that teaching yourself, by yourself, at home being less likely to widen your social circle, though!