I don't know actually.
Seen plenty of people who are otherwise phenomenal electrical engineers discuss it when teaching surface mount soldering but all I can think of just note it is somewhat self aligning (assuming you did not stick the chip down*, hold it down too hard or not get it all molten at once) and leave it at that.
I can cover the physical basis for it if you wanted, though would be just as easy to say "go look up the usual discussion of lowest possible energy state for surface area, usually done for bubbles aka why are bubbles round?" that they teach to 16-undergrad in physics/engineering as it is the same thing really.
Many years ago I did a very short bit with exotic solders and wetting of them/getting them to have nice wetting like good old lead-tin (can be done, expensive though) but never really had to categorise this alignment as much as flowing into a more mechanical type solder join.
*dab of superglue under a particularly annoying chip or component is done occasionally if dab of flux is not available or not working.