I'm not completely sure what the definition is.
Nobody is really sure what makes a friend, you can not see or talk to a person for years and still consider them a friend if asked what your relationship is.
My own theory of friendship is this, family are people you are related to by blood, therefore you accept all facets of their nature and will put up with their idiosyncrasies more so than you do with anybody else, then there are people in your life that you also do this with but that are not related by blood and so you call these people, friends.
On down the scale would be acquaintances whereby you may accept their nature but cannot endure their idiosyncrasies perhaps.
Associates, with whom you tolerate their foibles but don't necessarily accept their nature. Lastly, enemies, with these people you obviously cant understand their nature and wont accept or even tolerate their quirks.
These last people we tend to avoid but strangely, it isn't unknown for the human animal to keep their enemies close for a number of reasons and so that may even be called friendship (of a type).
So I think the key here is acceptance and understanding, with family, you think you have to understand and accept the way they are, but with strangers you don't need to understand or make acceptations for, and everything in between those to opposites is up for determination, placement on a scale depending on length of exposure, possibly.
Usually feeling develops with length of time and exposure to that person, so if you spend a lot of time with them they may remain unchanged in your orbit or become friends or enemies depending on how tolerant you feel towards them and your understanding of them as a character.
Conversely you may meet somebody and instantly be attracted to them in a non sexual way leading to a deep and long lasting friendship, this may have something to do with biology, pheromones and such, leading back to a more primal time when people would form packs for safety and greater ability in hunting, which has led us to modern social structure and hierarchy...
Which as an Aspie I am not to familiar with, hence me having no friends, so I am not a good judge of what constitutes friendship and you may disregard my opinion LOL
PS; Humans tend to bond more rapidly over humour and if you can make somebody laugh it may be a good sign that a closer dynamic is called for ; ]