Without using a torque wrench there are two possibilities. You over tightened them to the point of weakening the studs. And the strain eventually caused one or more to fail taking the rest with them. Or you did not tighten them properly, they worked loose, and the pounding of the loose wheel cause one or more to fail and take the rest with them.
Many people think if tight is good, then tighter is better, and stand on it is the best. Using a cheater bar is the ultimate. Not so. And inversely, not tight enough is not good either.